Preheat the oven to 400F (200C). Prick the bottom and sides of the pie crust then bake the crust for 10 min. Once the crust is baked, lower the oven temperature to 375F (190C).

In a skillet over medium heat, cook your bacon pieces until crispy, about 5-6 minutes. Set aside on a paper towel-lined plate, then remove most of the bacon fat from the pan, leaving about a tablespoon. Add your onion to the pan and cook stirring frequently for another 5-6 minutes, until the onions are soft and starting to brown. If they start to stick, add a splash of water.

In a measuring cup or small bowl, combine the milk and melted butter. Combine the milk mixture with the eggs in a large bowl and beat until the eggs and milk are fully combined. Add the salt, pepper, nutmeg, and cayenne if using.

Add your crumbled bacon, onions, and shredded swiss cheese to the bottom of your cooled crust. Carefully pour the egg mixture over the filling. I find this is easiest if your pie plate is on a baking sheet. You can add half the egg mixture, place the pan in the oven, and add the rest of the egg mixture once it is in the oven so you don't spill it.

Bake quiche for 35-40 minutes until the quiche is mostly set with a small wiggle in the center, or a knife inserted an inch from the crust comes out clean. Let cool for 10-15 minutes before slicing. Cool completely before storing.