For the Crust:

1. Whisk together the flour and salt in a large mixing bowl. Using a pastry cutter, cut the cold butter cubes into the flour mixture until the butter pieces are pea-size and coated entirely in flour.
2. Using your hands or sturdy spoon, knead in the creme fraiche just until a thick dough begins to form. If there is an excess amount of dry ingredients remaining at the bottom of the bowl, gradually pour in the water as you mix to bind the dough together.
3. Turn the dough onto a clean counter dusted with flour and press lightly to form a smooth, flat disc. Tightly wrap the disc in plastic wrap and refrigerate for at least 1 hour.
4. Set out a 9-inch tart pan with a removable bottom. Remove the chilled dough from the refrigerator and let sit at room temperature for 5-10 minutes, until it has softened slightly and is pliable. Remove the plastic wrap and place the disc on a clean counter dusted with flour.
5. With a rolling pin, roll and flatten the dough until it is about 1/8 inch thick and is large enough to cover the bottom and sides of the tart pan with an inch of excess around the edges.
6. Carefully transfer the dough to the tart pan. Press into the bottom of the pan, then press into the sides. Trim any excess dough around the edges so the dough is flush with the top of the sides of the pan.
7. Pierce the bottom of the dough several times with the tines of a fork. Place the pan uncovered in the freezer and chill for 1 hour until very cold and firm.
8. Preheat the oven to 400°F. Cover the bottom and sides of the tart pan with a sheet of parchment paper and fold the excess over the sides for easy lifting later. Gently press the paper against the bottom and sides of the pan, and spread pie weights out evenly to cover the bottom. 
9. Transfer the pan to the oven and bake for 20-25 minutes. Lift the parchment paper to remove the hot pie weights and set aside to cool.
10. Place the pan back in the oven and bake for another 10 minutes or until very lightly golden brown. Remove the pan from the oven and let cool completely on a wire rack as you prepare the filling. Keep the oven on, set to 400°F.

For the Filling:

1. Cook the bacon in a large skillet on medium-low heat until browned and crispy, flipping once, about 5-7 minutes.
2. Set the cooked bacon aside on a paper towel-lined plate to collect grease and cool. Drain the majority of the bacon grease from the pan, wipe out any brown or burned bits of bacon, and leave a thin film behind to coat the pan. Place the pan back on the stovetop over medium-high heat.
3. Add the onion to the skillet and season with the salt. Saute, stirring occasionally, until the onions become translucent, soften slightly, and just start to caramelize, about 5 minutes. Remove from heat and transfer the onions to a plate to cool.
4. Roughly chop the bacon.
5. Whisk together the eggs, creme fraiche, and black pepper in a large bowl. Whisk in the cooled onions and chopped bacon.

To Assemble and Bake:

1. Pour the filling into the parbaked tart crust.
2. Immediately transfer the pan to the oven and bake for 40-45 minutes, until the mixture is bubbling and the crust is deep golden brown.
3. Remove the tart from the oven and place on a wire rack to cool and set for 30 minutes..
4. Release the removable sides of the pan and serve warm. Leftovers that have cooled completely may be refrigerated for up to 5 days, or frozen for up to 6 months, in an airtight plastic container or wrapped tightly in plastic wrap.