1. Prepare the Crust:

• Combine Dry Ingredients: In a large bowl, whisk together the flour and salt.
• Incorporate Butter: Add the chilled, cubed butter to the flour mixture. Using a pastry blender or your fingertips, cut the butter into the flour until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining. This step is crucial for flakiness. Avoid overworking the dough.
• Add Ice Water: Gradually add the ice water, one tablespoon at a time, mixing gently with a fork until the dough just comes together. Be careful not to add too much water; you want a dough that is moist but not sticky.
• Form Dough and Chill: Gather the dough into a disc, wrap it tightly in plastic wrap, and flatten it slightly. Refrigerate for at least 30 minutes, or up to 2 hours. Chilling allows the gluten to relax, resulting in a more tender crust.
• Roll Out Dough: On a lightly floured surface, roll out the chilled dough into a 12-inch circle, about ⅛-inch thick.
• Transfer to Pie Dish: Gently transfer the dough to a 9-inch pie dish. Press the dough into the bottom and up the sides of the dish. Trim any excess dough and crimp the edges decoratively.
• Pre-bake the Crust (Blind Bake): Preheat oven to 375°F (190°C). Line the crust with parchment paper and fill with pie weights or dried beans. This prevents the crust from puffing up during pre-baking. Bake for 15 minutes. Remove the parchment paper and pie weights and bake for another 10 minutes, or until the crust is lightly golden. This pre-baking step ensures a crisp bottom crust. Let the crust cool slightly while you prepare the filling.

2. Prepare the Filling:

• Cook Bacon and Onion: In a skillet over medium heat, cook the diced bacon until crisp. Remove the bacon with a slotted spoon and set aside, reserving about 1 tablespoon of bacon fat in the skillet. Add the chopped onion to the skillet with the bacon fat and cook until softened and translucent, about 5-7 minutes. Do not brown the onions.
• Whisk Eggs and Dairy: In a large bowl, whisk together the eggs, heavy cream, and milk until well combined.
• Season Custard: Stir in the grated Gruyère cheese, nutmeg, salt, and freshly ground black pepper. Taste and adjust seasoning as needed.
• Assemble Quiche: Sprinkle the cooked bacon and sautéed onions evenly over the bottom of the pre-baked crust. Pour the egg mixture over the bacon and onions, ensuring it is evenly distributed.

3. Bake the Quiche:

• Bake: Bake in the preheated oven at 350°F (175°C) for 35-45 minutes, or until the custard is set and the crust is golden brown. The quiche is done when the center is just set and jiggles slightly when gently shaken. If the crust is browning too quickly, you can loosely tent it with aluminum foil.
• Cool and Serve: Let the quiche cool in the pie dish for at least 10-15 minutes before slicing and serving. This allows the custard to set further and makes slicing easier.