Preheat the oven at 180C (375F).
Place the pie crust on a baking pan and pierce lightly all over with a fork (around 2 inches apart).
Beat the eggs, milk, and heavy cream in a large bowl, along with the salt and pepper.
Cook the bacon in a frying pan for a few minutes.
Add the mushrooms and onions into the pan to lightly sauté them as well.
Remove the bacon, mushrooms and onions from the stove.
Add the bacon, cheese, salt, pepper, and any optional ingredients into the egg mixture.
Spread the mixture across the pie crust.
Sprinkle across the top a pinch of nutmeg.
Place in the oven for 45 minutes or until the top crust is browned.
Serve while warm.