Preheat the Oven: Preheat your oven to 375°F (190°C).
Prepare the Crust: Roll out the pie crust and fit it into a 9-inch pie dish. Trim any excess dough and crimp the edges. If using a pre-made crust, follow the package instructions for pre-baking. To prevent the crust from puffing up, prick the bottom with a fork or use pie weights. Bake the crust for about 10 minutes, until lightly golden. Remove from the oven and set aside.
Cook the Bacon: While the crust is baking, cook the bacon in a skillet over medium heat until crispy. Transfer the bacon to a paper towel-lined plate to drain, then crumble it into small pieces.
Prepare the Egg Mixture: In a mixing bowl, whisk together the eggs, milk, heavy cream, salt, pepper, and ground nutmeg (if using) until well combined.
Assemble the Quiche: Sprinkle the crumbled bacon evenly over the pre-baked crust. Add the shredded cheese on top of the bacon. Pour the egg mixture over the cheese and bacon, making sure it's evenly distributed. If using green onions, sprinkle them on top.
Bake the Quiche: Place the quiche in the oven and bake for 35-40 minutes, or until the center is set and the top is golden brown. To check for doneness, insert a knife into the center of the quiche; it should come out clean. If the edges of the crust start to brown too quickly, cover them with aluminum foil.
Cool and Serve: Remove the quiche from the oven and let it cool for about 10 minutes before slicing. Serve warm or at room temperature.