Making the Crust:

1. Pulse Dry Ingredients: Begin by combining the dry ingredients in your food processor. Place 1 cup of all-purpose flour and ½ teaspoon of kosher salt into the bowl of a food processor. Pulse a few times until these ingredients are just combined. This ensures the salt is evenly distributed throughout the flour.
2. Incorporate Cold Butter: Now, add the star ingredient for a flaky crust: cold butter. Scatter the 1 stick (8 tablespoons) of cold unsalted butter, cut into small pieces, over the flour mixture in the food processor. Pulse in short bursts, about 8-10 times, until the mixture resembles coarse cornmeal. You should still see small pieces of butter, which is exactly what you want for flakiness. Avoid over-processing at this stage, as it can lead to a tough crust.
3. Add Ice Water Gradually: This is where the magic happens. Sprinkle 3 tablespoons of ice water over the flour-butter mixture. Pulse again, a few seconds at a time, until the dough just starts to come together. It should look slightly crumbly but begin to clump.
4. Test Dough Consistency: To ensure the dough is ready, pinch a small amount between your fingers. If it holds together, it’s perfect. If it’s still too dry and crumbly, add more ice water, 1 tablespoon at a time, and pulse a couple more times after each addition. Be careful not to add too much water, as this can make the dough sticky. Aim for a dough that is just moist enough to hold together.
5. Form Dough Disc and Chill: Once the dough has come together, transfer it to a sheet of plastic wrap. Gently pat it into a disc about 1 inch thick. Wrap it tightly in the plastic wrap. Now, the crucial step: refrigerate the dough for at least 1 hour, or preferably overnight. This chilling time allows the gluten in the flour to relax, making the dough easier to roll out and preventing shrinkage during baking. Cold butter also helps maintain flakiness.
6. Roll Out Dough: When you’re ready to bake, remove the dough from the refrigerator. Lightly flour a clean work surface and your rolling pin. Place the chilled dough disc on the floured surface and roll it out into an 11-inch round that’s about ⅛-inch thick. Work from the center outwards, rotating the dough occasionally to ensure an even circle. If the dough starts to stick, add a little more flour to your work surface and rolling pin.
7. Line Tart Pan: Carefully transfer the rolled-out dough to a 9-inch fluted tart pan with a removable bottom. Gently press the dough into the bottom and up the sides of the pan, ensuring it fits snugly into the flutes. Leave an even overhang of dough all around the rim.
8. Trim Excess Dough: To create a neat and professional edge, roll a rolling pin firmly over the top of the tart pan. This will cut off the excess dough, leaving a clean edge. Discard the excess dough (or save it to make small cookies if you’re feeling creative!).
9. Prick Crust and Chill Again: Use a fork to prick the bottom of the crust all over. This prevents the crust from puffing up during baking. Return the lined tart pan to the refrigerator to chill for another 30 minutes. This second chilling step helps prevent shrinkage even further.
10. Preheat Oven and Prepare for Blind Baking: Position an oven rack in the lower third of your oven and preheat the oven to 375°F (190°C). This lower rack position will ensure the crust bakes evenly from the bottom up.
11. Blind Bake with Weights: To prevent the crust from slumping and to ensure it cooks evenly, we need to blind bake it. Press a piece of parchment paper or aluminum foil over the chilled crust, making sure it covers the entire surface. Fill the parchment or foil with pie weights, dried beans, or rice. These weights will prevent the crust from puffing up during baking. Place the tart pan on a baking sheet for easier handling and to ensure even heat distribution.
12. First Bake: Bake the crust in the preheated oven for about 40 minutes, or until the edges are golden brown. The center may still look slightly pale at this point.
13. Remove Weights and Second Bake: Carefully remove the baking sheet from the oven. Gently lift out the parchment paper and pie weights (or beans/rice). Return the crust to the oven for another 15 minutes, or until the bottom of the crust is dry and slightly golden. This second bake without weights ensures the crust is fully cooked and crisp.
14. Cool Crust: Once baked, remove the crust from the oven and let it cool completely in the tart pan for about 30 minutes. This allows the crust to firm up and makes it easier to handle when adding the filling.

Making the Filling:

1. Sauté Onions: While the crust is cooling, prepare the filling. In a medium skillet, melt 1 tablespoon of unsalted butter over medium-low heat. Add the thinly sliced yellow onion, ½ teaspoon of kosher salt, and ½ cup of water to the skillet.
2. Cook Onions Slowly: Cook the onions over medium-low heat for about 30 minutes, stirring occasionally. The water will help steam the onions initially, then evaporate as they soften and caramelize. Continue cooking until the onions are completely softened, translucent, and slightly golden. Slow cooking brings out their natural sweetness.
3. Cook Bacon: While the onions are cooking, prepare the bacon. In a separate medium skillet set over medium-low heat, cook the 4 ounces of bacon, cut into ½-inch pieces. Cook for about 10-15 minutes, stirring occasionally, until the bacon is crisp and the fat has rendered. Cooking over medium-low heat prevents the bacon from burning and allows it to crisp up nicely.
4. Combine Onions and Bacon: Once the onions are cooked and the bacon is crisp, use a slotted spoon to transfer the bacon to the skillet with the onions. This leaves behind most of the bacon fat in the bacon skillet.
5. Add Thyme and Pepper: Stir in 1 teaspoon of fresh thyme leaves and ½ teaspoon of freshly ground black pepper to the onion and bacon mixture. These aromatics enhance the flavor profile of the filling.
6. Assemble Quiche: Spread the onion and bacon mixture evenly over the bottom of the cooled pre-baked crust. Sprinkle the ½ cup of shredded Gruyere cheese evenly over the onion mixture.
7. Prepare Egg Mixture: In a medium bowl, whisk together 1 cup of heavy cream, 2 large eggs, and ½ teaspoon of kosher salt until well combined and slightly frothy. Whisking ensures the eggs and cream are fully incorporated and creates a smooth custard base.
8. Pour Filling and Garnish: Carefully pour the egg mixture evenly over the filling in the crust, ensuring it reaches all corners. Sprinkle the remaining 1 teaspoon of fresh thyme leaves over the top of the quiche for a final touch of flavor and visual appeal.
9. Bake Quiche: Place the baking sheet with the quiche in the oven. Bake in the preheated oven at 375°F (190°C) for about 30 minutes, or until the quiche is set and golden brown on top. The center should be just set and not jiggly.
10. Cool Before Serving: Once baked, remove the quiche from the oven and let it cool for at least 30 minutes before slicing and serving. This cooling time allows the quiche to set completely and makes it easier to cut into clean slices. It also allows the flavors to meld together beautifully.