Savory German Onion Tart (Zwiebelkuchen)

It’s time to bring onions into the spotlight with this German onion tart.

Onions are often relegated to the role of add-ins, and they rarely get a chance to play the leading part in a recipe.

But this tart is going to change your perspective!

Also known as Zwiebelkuchen, this German onion pie is a hearty, oven-baked dish filled with onion and bacon that is perfect to serve throughout the fall months, and on the first cold nights of winter.

This savory pastry is well-loved in Germany, especially in wine-growing states like Rhineland-Palatinate. The area has an excellent reputation around the world for its cuisine and festivals.

During autumn in the US, you will find many wine festivals and restaurants that serve a version of this onion pastry with white wine – and they definitely make an excellent duo!

While there are multiple interpretations of the dish to choose from, from deep-dish pies to rustic flatbreads, I love balancing the hearty flavors of the filling with a more delicate pastry crust to serve it as a tart.

The flaky, buttery crust, given a tasty boost with creme fraiche, is the ideal vessel to house all of the rich and savory ingredients.

I render bacon fat to lightly saute the sliced onions in my version. While caramelizing them, the sulfurous scent and pungent flavor of the onions takes a delicious turn in a softer, slightly sweeter direction.

The cooked onions and bacon are combined with eggs and creme fraiche to create a custardy, mouthwatering filling.

After baking and cutting into slices it’s traditionally eaten warm, but this tart can also be consumed after chilling in the refrigerator or at room temperature. The tart also freezes well, and can be warmed in the oven after it has thawed.

Concerning side dishes, there are many tasty options available to you.

A fresh, green salad is a nice complement to the big flavors in the tart. But I highly recommend serving it with roasted root vegetables and a glass of wine so you can really enjoy and experience the celebratory theme of an autumnal festival!

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Cooking by the Numbers…

Step 1 – Prep the Dough

Set out a rolling pin and a 9-inch metal tart pan with a removable bottom.

Measure out the all-purpose flour, salt, creme fraiche, and water for the crust.

Cube the stick of unsalted butter using a sturdy cutting board and sharp knife.

Keep your cold ingredients as cold as possible! Your water, creme fraiche, and butter should be chilled and they should stay in the refrigerator until you’re ready to use in the recipe.

A cold temperature for these ingredients will ensure your tart dough will bake into a flaky, yet sturdy, well-formed crust.

Step 2 – Make and Chill the Dough

In a large mixing bowl, whisk together the flour and salt.

Use a pastry cutter to cut in the cubes of butter until the pieces are pea-sized and evenly coated in flour. Using your hands or sturdy spoon, mix in the creme fraiche until a thick dough starts to form. Don’t overmix the dough, or else it may toughen and shrink while baking.

Do you see an excess pile of dry ingredients at the bottom of the bowl that is not incorporated into the main mound of dough? Gradually pour in the cold water as you mix to bind everything together, using only what you need.

Dust a clean work counter with flour and place the dough on top. Press lightly to form a smooth, flat disc.

Forming the dough into a disc is an essential step you can take now to help you later! The flat disc is the best shape to start with before rolling it out into a large, flat circle to fill the tart pan in the following steps.

Tightly wrap the disc in plastic wrap and place in your refrigerator. Chill for at least 1 hour.

Step 3 – Roll the Dough

Remove the chilled dough from the refrigerator and let it sit at room temperature for 5 to 10 minutes.

You don’t want to attempt to roll it out immediately as it will be too cold and stiff, and will rip easily. Letting it sit for a few minutes will soften the dough to an ideal temperature that’s pliable enough for rolling.

Remove the plastic wrap and place the disc on a clean countertop dusted with flour.

Roll and flatten the dough into an even circle using a rolling pin until it is about 1/8 inch thick. It should be large enough to cover the base of the tart pan, with about 1 inch of excess dough around the edges.

Do you need some help determining if you have reached the right size? You can hover the tart pan over the dough to see if you need to continue rolling.

Step 4 – Form into the Pan, Dock, and Chill

Carefully transfer the dough to the tart pan. An easy way to do this without disastrously ripping the dough is to gently fold the dough in half, quickly transfer it to one half of the tart pan, and unfold it over the other half.

Using your hands, gently press the dough into the bottom of the pan, then press it onto the sides of the pan.

Trim all excess dough around the edges so the dough is flush with the top of the tart pan’s sides. A quick technique for this is to roll a rolling pin over the edges of the tart pan to create the cleanest cut.

Evenly pierce the bottom of the dough multiple times using the tines of a fork. This will help air escape from the bottom of the pan, allowing the dough to remain flat and bake evenly without forming large air bubbles.

Place the pan uncovered in the freezer and chill for 1 hour until very cold and firm.

Don’t be skimpy with this chill time! This helps to set the structure of the dough in the tart pan so the butter won’t melt prematurely and cause the dough to collapse while baking.

Step 5 – Blind Bake

When the crust is nearly finished chilling, preheat the oven to 400°F.

Take the pan out of the freezer and cover the tart pan with a sheet of parchment paper to cover the bottom and create a bit of an overhang that goes up and over the sides. Place pie weights on top of the paper.

For pie weights, you can use uncooked rice, dried beans, or granulated sugar. You can also purchase ceramic pie weights, available on Amazon. I would advise buying two containers so you have enough to weigh down your crust as it bakes!

Take your pick. As long as you use enough to reach as close to the top of the tart pan as possible without the weights spilling over, this will ensure the sides of the dough will stay in place and won’t collapse.

Transfer the pan to the oven and bake for 20 to 25 minutes.

Take out the tart pan and carefully remove the parchment paper, lifting it up around the edges so it holds the weights – be careful, because they will be hot! Transfer the pan back to the oven and bake for another 10 minutes, or until the crust is very lightly golden brown.

You don’t want to develop too much color with the crust at this stage, since it will continue to bake after filling.

Remove the pan from the oven and let the crust cool completely – keeping it in the pan – as you prepare the filling. Keep the oven on.

Step 6 – Prep the Filling

As the crust is cooling, you can now prepare and make the filling.

Measure out the salt, black pepper, and creme fraiche. Crack the two eggs into a small bowl, checking for shell fragments.

Thinly slice two white onions. Learn how to avoid the tears, and how to properly select, store, and prep an onion.

Take out 6 ounces of thick-cut bacon. This will equate to about 6 slices of bacon.

Step 7 – Cook the Bacon

Place the bacon in a large skillet in a single layer. If it doesn’t all fit, you can cook the bacon in batches.

Cook on medium-low heat, flipping once for even cooking, until the bacon is browned and crispy. This will take about 5 to 7 minutes. The bacon will be mixed into a wet filling, so the bacon should be well-cooked to maintain some texture.

Remove the bacon from the skillet, and place the slices on a large plate or platter lined with paper towels to soak up any excess grease. Allow them to cool as you cook the onions. When cooled, roughly chop into small pieces.

Drain the majority of the bacon grease from the pan, and wipe out any burned pieces of bacon. Leave a thin film for sauteing the onions in the next step. You can reserve the extra grease for another recipe, like Foodal’s whole wheat flatbread with salad and bacon honey mustard dressing.

Place the pan back on the stovetop and increase the heat to medium-high.

Step 8 – Cook the Onions

Combine the onion slices and salt in the skillet.

Saute the onions until they soften slightly and just start to develop some color, about 5 minutes. Stir the onions occasionally while they cook. You don’t want them to become too soft or too deeply caramelized, as they will continue to cook in the tart.

Transfer the onions to a large plate and set aside to cool completely. You do not want to add hot onions to the custard filling, or the eggs may curdle.

Step 9 – Make the Custard

As the onions are cooling, make the custard by whisking together the eggs, creme fraiche, and black pepper together in a large bowl until combined.

Whisk in the onions and bacon until distributed evenly throughout – you can reserve about 1/4 cup of the chopped bacon to sprinkle on top of the tart just before serving for some extra crunch! Otherwise, add it all in now!

Step 10 – Assemble

Pour the filling into the parbaked tart crust. You can use a spatula to spread the onions evenly around the pan if they have collected in the middle.

Use a soft utensil like a rubber spatula to avoid scraping the bottom of the dough!

Step 11 – Bake, Cool, and Serve

Immediately transfer the pan to the oven. Bake until the mixture is bubbling and the crust is a deep golden brown. This will take about 40 to 45 minutes.

Remove the tart from the oven and let it cool for 30 minutes on a wire rack in the pan before carefully releasing the sides.

And don’t forget to gaze upon the beautifully golden crust, the end result of all your hard work making tart dough from scratch!

You can serve slices while they’re still warm, or allow the tart to cool completely and store it in the refrigerator for up to five days wrapped tightly in plastic or in an airtight container.

For freezer storage, allow to cool completely at room temperature before wrapping in plastic wrap, and freeze for up to 6 months.