Step 1: Prepare the Crust

• Combine dry ingredients: In a food processor, pulse together the flour, salt, and sugar.
• Add butter: Add the diced butter and pulse until the mixture resembles coarse crumbs.
• Add water: Gradually add ice water, one tablespoon at a time, pulsing until the dough just comes together.
• Chill the dough: Form the dough into a disc, wrap it in plastic wrap, and refrigerate for at least 30 minutes.

Step 2: Prebake the Crust

• Preheat the oven: Preheat your oven to 375°F (190°C).
• Roll out the dough: Roll the chilled dough into a 12-inch circle and fit it into a 9-inch tart pan with a removable bottom. Trim the edges.
• Blind bake the crust: Line the crust with parchment paper, fill it with pie weights or dried beans, and bake for 15 minutes. Remove the weights and parchment, then bake for another 5 minutes. Set aside to cool.

Step 3: Cook the Bacon and Onions

• Cook the bacon: In a skillet, cook the diced bacon over medium heat until crisp. Remove with a slotted spoon and drain on paper towels.
• Sauté the onions: In the same skillet, cook the chopped onions in the bacon drippings until softened, about 5 minutes. Set aside.

Step 4: Prepare the Custard Filling

• Whisk the custard: In a mixing bowl, whisk together the eggs, heavy cream, salt, pepper, and nutmeg until smooth.

Step 5: Assemble the Quiche

• Layer the ingredients: Sprinkle the cooked bacon, sautéed onions, and grated Gruyère cheese evenly over the cooled crust.
• Add the custard: Pour the egg and cream mixture over the filling ingredients, ensuring it spreads evenly.

Step 6: Bake the Quiche

• Bake: Place the quiche in the preheated oven and bake for 35–40 minutes, or until the custard is set and the top is lightly golden.
• Cool: Allow the quiche to cool for 10–15 minutes before slicing and serving.

Step 7: Serve

• Slice and serve: Serve warm or at room temperature with a side salad or roasted vegetables.