Blueberry Oatmeal Squares

Butter, brown sugar, and cinnamon: Has anything ever come from this trio that wasn’t undeniably delicious?

Vertical image of a stack of blueberry bars on a white plate, with text on the top and bottom of the image.

Go ahead. Take your time trying to think of something. I’ll be here picking oat crumbs off of my sweatpants.

Although I consider myself much more of a savory enthusiast who favors cooking, rather than a fanatic for the very structured world of baking, there are certain sweet recipes I find myself falling for.

Especially ones that are outrageously easy to prepare.

Sweet treats that are too one-note just don’t do it for me, but when a few complex flavors are sprinkled into the mix, my taste buds are fully on board.

These tart blueberry oatmeal squares are the perfect example of this. Maybe it’s the bright citrus juice and warm, woody vanilla in the jammy blend, or maybe it’s the lemon zest-laced toasted oats.

There’s something special about these sweet treats, and it’s definitely not Maybelline.

Vertical image of fruit bars, some on their sides, on a wooden cutting board next to a bowl of fresh fruit.

But the earthy cinnamon, caramel-scented brown sugar, and rich butter top it all off, and I just can’t get enough – the aroma of these ingredients is the first thing my nose picks up once the pan is slid into the oven and the heat starts doing its thing.

As far as the fruity layer goes, it’s no secret that blueberry and lemon go way back. The citrus adds a refreshing element, and the acid enhances the blueberry’s mild tartness.

A perfect pair, if I do say so myself, and the two work together like old friends. Sweetened with sugar and thickened with a cornstarch slurry, the combination is nothing short of magical.

As far as the “dry mixture” goes, it’s a piece of cake.

(Well, actually, it’s an oatmeal square…)

If this is one of your first rodeos with a sweet baked recipe and you’re unfamiliar with terms like “cut in the butter,” don’t worry. It’s not complicated. And you don’t need scissors.

Vertical image of stacks of fruit bars on a white plate next to a bowl of fresh fruit.

Cutting in the butter is just a fancy term for combining the dry ingredients with the fat as swiftly as possible. No pastry cutter for the job? No problem. I use two butter knives to create those coarse little crumbs.

The result is small butter nuggets coated with flour, lemon zest, and brown sugar that evenly dance their way throughout the oats.

Why do you need the butter to be evenly dispersed? Well, would you rather have a piece of toast with one giant wad of butter in the middle, or one with butter spread evenly from edge to edge?

Case closed. And now I want toast.

The truth is that there’s really only one difficult part of this process. And that’s the waiting.

Full disclosure here: The fruit filling needs to chill and thicken up in the fridge before being added to the pan, the perfect bake time happens to fall at just under an hour, and once your fragrant, golden-brown masterpiece is pulled from the oven, it needs another hour to set and cool.

Vertical top-down image of fruit bars on a white plate on a wooden table next to a blue napkin and blue bowl.

But good things come to those who wait. And trying to slice into it seconds after it comes out of the oven will only result in a messy crime scene of gooey blueberry liquid. Nobody wants that!

Don’t fret. It will be worth every second when you sink your teeth into these sweet, chewy squares.

Bring some patience and try to remember that you’ll be meeting all these wonderful ingredients at the finish line. I promise you won’t even mind the down time.

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Horizontal image of a stack of fruit bar cookies on a wooden cutting in front of bowls of ingredients and a blue napkin.

Blueberry Oatmeal Squares

  • Author: Fanny Slater
  • Total Time: 3 hours, 30 minute
  • Yield: 12 squares 1x


Lemon zest adds a pop to these blueberry, brown sugar, and oatmeal squares. They’re perfect for breakfast, dessert, or a quick snack.


  • 3 cups fresh blueberries
  • 1/2 cup granulated sugar
  • 1 teaspoon vanilla extract
  • 3 tablespoons lemon juice (from about 1 large)
  • 4 teaspoons cornstarch
  • 2 tablespoons cold water
  • 2 1/2 cups rolled oats
  • 1 1/4 cups all-purpose flour
  • 3/4 cup packed light brown sugar
  • 1 tablespoon lemon zest (from about 1 large)
  • 1/4 teaspoon coarse salt
  • 1 1/4 teaspoons ground cinnamon
  • 2 sticks (1 cup) cold unsalted butter, cubed


  1. Preheat the oven to 350°F. Line an 8-inch square cake pan with parchment paper to create a sling for easy removal. Spray with non-stick cooking spray.
  2. In a medium saucepot over medium-high heat, add the blueberries, granulated sugar, vanilla, and lemon juice. Stir to combine. When the blueberries begin to release their juices, allow the liquid to come to a boil. Reduce the heat to medium-low and simmer, stirring occasionally, until the berries are broken down and tender, about 10 minutes.
  3. While the blueberries are cooking, whisk the cornstarch with the water until blended in a small bowl. Gradually stir the cornstarch slurry into the blueberry mixture and continue stirring until the mixture is visibly thickened, about 1 minute. Remove pot from heat. Transfer the blueberry mixture to a bowl and cool to room temperature on the counter. Then refrigerate until chilled, about 1 hour.
  4. In a large mixing bowl, stir the oats, flour, brown sugar, lemon zest, salt, and cinnamon together until combined. Using a pastry blender (or two butter knives), cut in the butter until the mixture has the texture of coarse crumbs.
  5. Firmly press half of the crumbs into the bottom of the prepared pan to create a smooth, even layer. Top with the blueberry filing, and then scatter the remaining oat mixture on top. Press down lightly to make sure it adheres.
  6. Bake until the edges are set and the top layer of crumbs is a light golden color, about 50-55 minutes. Remove from the oven and place on a wire rack.
  7. Cool completely in the pan, about 1 hour at room temperature, and then use the ends of the parchment paper to help lift the bars out of the pan. Slice into even squares and serve.
  8. Store leftover blueberry squares in an airtight container in the fridge for up to 1 week.
  • Prep Time: 25 minutes
  • Cook Time: 1 hour, 5 minutes
  • Category: Bars
  • Method: Stovetop/Baking
  • Cuisine: Snacks

Keywords: blueberry, oat, oatmeal, squares, bars

Cooking By the Numbers…

Step 1 – Gather and Measure Ingredients

Preheat the oven to 350°F and make a parchment sling to line an 8-inch square cake pan by cutting one or two pieces of parchment paper about 10-inches long so they fit the width of the pan and extend 1-2 inches over two of the sides (creating handles for easy removal). Spray the paper with non-stick cooking spray.

Horizontal image of large and small bowls filled with assorted ingredients, a measuring cup filled with pats of butter, and a zester and lemon on a towel.

Rinse the fruit, juice and zest the lemon, and cube the 2 sticks of butter.

The butter should be cold and straight from the fridge so it disperses evenly and doesn’t just melt into the oats and flour. Keep the cubed butter in the fridge until you’re ready to use it.

Measure the sugar, vanilla extract, lemon zest and juice, cornstarch, cold water, oats, flour, packed brown sugar, salt, and cinnamon.

Step 2 – Make and Thicken the Fruit Filling

Add the blueberries, sugar, vanilla, and lemon juice to a medium saucepot over medium-high heat. Stir to combine. The blueberries will start to break down and release their juices into the pan.

Horizontal image of pouring a slurry into a pot with a compote stirred by a whisk.

Once the liquid comes to a boil, reduce the heat to medium-low and simmer, stirring occasionally, until the mixture is juicy, thickened, and a little darker, about 10 minutes.

While the fruit is cooking, make the cornstarch slurry by whisking the cornstarch with the cold water in a small bowl until thoroughly blended. Whisking as you pour, gradually add the slurry to the fruit mixture. Continue stirring until the mixture has visibly thickened, about 1 minute, and then remove the pot from heat.

Horizontal image of whisking a dark purple fruit compote mixture in a pot.

Transfer this mixture to a bowl and let it cool to room temperature on the counter. Refrigerate until chilled, about 1 hour.

Step 3 – Make the Bottom Oatmeal Layer

Add the oats, flour, brown sugar, lemon zest, salt, and cinnamon to a large mixing bowl and stir until well-combined.

Horizontal image of a pressed unbaked crust in a square pan lined with parchment paper.

Cut in the cold butter using either a pastry blender or two butter knives until the pieces of flour-coated butter are small and have the texture of coarse crumbs.

Pressing down to get a flat, even layer, use your fingers to line the bottom of the prepared baking pan with half of the oat mixture.

Step 4 – Add the Fruit Filling, Top, and Bake

Pour and spread the blueberry filing over the smooth oat layer. Scatter the remaining oat mixture on top. Gently press down to adhere the oats to the spread, but not pushing so hard the liquid seeps through.

Horizontal image of a blueberry compote in a square pan lined with paper.

Bake until the top is light-golden brown and the edges are set, about 50 to 55 minutes. You’ll see some of the filling creeping out around the sides.

Remove the pan from the oven and place it on a wire rack to allow for even air distribution on the bottom of the pan as it cools. No soggy bottoms here!

Horizontal image of an unbaked streusel topping in a square pan lined with paper.

Allow the squares to cool completely in the pan, for about 1 hour at room temperature. If you try to slice the bars before they’ve cooled and set completely, they’ll crumble apart.

Once cooled, grab the ends of the parchment paper and lift the squares out of the pan. Slice into 12 evenly-sized pieces and serve.

Horizontal image of slices and squares of a baked good with a purple filling.

You can store any leftover squares in an airtight container in the fridge for up to 1 week, or individually wrap and freeze squares for a quick breakfast, snack, or dessert.

So Many Ways to Serve!

At first glance, these rich, melt-in-your-mouth berry bars may seem to have more appeal as a dessert. But with the main ingredients being blueberries and oatmeal, tell me a cup of French roast coffee wouldn’t pair with one of these like a charm.

Horizontal close-up image of fruit bars on a wooden board lined with parchment paper.

If it’s a final course you’re after, I suggest teeing these up with a mound of vanilla bean ice cream or gelato on top, with a sprig of fresh mint for color.

As a quick snack, having the squares individually wrapped and stocked in the freezer for on-the-go emergencies is a brilliant plan. You can thank me later.

Horizontal image of a stack of fruit bar cookies on a wooden cutting in front of bowls of ingredients and a blue napkin.

What time of day will you scarf down your squares? Share your serving suggestions in the comments below! And don’t forget to give this recipe a five-star rating if you loved it.

Blueberries are a superfood that does a body good. Try some of these delicious recipes showcasing the sweet orbs next:

Photos by Fanny Slater, © Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Originally published by Lorna Kring on July 16, 2015. Last updated on June 23, 2022.

Nutritional information derived from a database of known generic and branded foods and ingredients and was not compiled by a registered dietitian or submitted for lab testing. It should be viewed as an approximation.

About Fanny Slater

Fanny Slater is a home-taught food enthusiast based in Wilmington, North Carolina who won the “Rachael Ray Show” Great American Cookbook Competition in 2014, and published her cookbook “Orange, Lavender & Figs” in 2016. Fanny is a food and beverage writer, recipe developer, and social media influencer. She was a co-host on the Food Network series “Kitchen Sink,” was featured on Cooking Channel’s longtime popular series “The Best Thing I Ever Ate,” and continues to appear regularly on the “Rachael Ray Show.”

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