Preheat oven to 425 F/218 C. Poke the bottom of the pie crust with a fork, then line with aluminum foil (or pie weight of choice). Bake for 15 minutes.
After crust has prebaked, lower oven temperature to 350 F/177 C.
Using a handmixer or whisk, beat eggs and milk until well combined. Add cheeses, salt, pepper, chopped/sauteed vegetables and chopped meat. If using leafy greens like spinach, set them aside.
If all ingredients are combined with the egg mixture, carefully pour the mixture into prebaked pie crust. If using leafy greens, pour half of the mixture into the crust, add leafy greens, then pour remaining mixture over top of them.
Bake at 350 F/177 C for 40-50 minutes, until the quiche is domed and a knife inserted into the middle reveals the egg mixture is completely cooked. Allow quiche to cool for about 10 minutes, then slice and serve. Keep leftovers refrigerated and covered.