Sauté onions in butter till clear.
Beat eggs with milk till frothy.
Add remaining ingredients and mix until well combined.
Pour into prepared pie shell.
~May also add other optional ingredients as desired, such as broken pieces of vegetarian sausage, sautéed zucchini and/or sliced mushrooms (sautéing first will get rid of a lot of the moisture in these), blanched broccoli, olives, etc.
Bake on a cookie sheet at 375° for 45-60 minutes or till a sharp knife inserted in the center comes out clean.
If the top starts to brown to much, cover with foil for the remainder of the baking time.