Add the flour, salt, and sugar to a large bowl. Mix together. Add the cubed butter to the flour. Using a dough cutter or fork, mix (or cut) the butter into the flour. Add 1 tablespoon of water at a time to start to form the dough. Once a ball is formed, flatten the dough into a disc and wrap it in plastic wrap. Refrigerate for at least 30 minutes.

Preheat the oven to 400℉. Spray a 9-inch pie pan with cooking spray and set aside.

Roll the pie dough out into a 12-inch circle. Transfer the dough to the pie pan and push it in to fit. Using a fork, pierce the crust several times.

Bake the crust for 10 minutes. Remove from the oven and allow to cool for 15 minutes. Reduce the oven temperature to 375℉.

Add the eggs, milk, salt, pepper, and cayenne to a large mixing bowl and whisk together. Set aside.

Place the crumbled bacon, gruyere cheese, and onion into the cooled pie crust.

Next, transfer the egg mixture to the pie crust. Bake for 20-25 minutes.

Allow the quiche to cool slightly before serving.