Frittatas are simple preparations, but a creamy custard base and two or three well-chosen ingredients can yield an egg dish on par with the silkiest French omelet and crustless quiche. When weighed down with too many ingredients, the custard loses its lift, the dish loses its focus, and the frittata becomes an egg casserole. Try to use equal parts of the flavoring ingredients for balance but don't stress if you can't -- feel free to use any fresh ingredients you have on hand. A cast-iron skillet is a must for simplicity -- you can go from stove to oven to table without changing pans.
Beat whole eggs, a few shavings of cold butter and milk until frothy, about 3 to 4 minutes. You need 6 eggs with 1 tablespoon of milk for a 10-inch frittata; use 8 eggs for a 12-inch skillet.
Add secondary flavoring ingredients to the eggs. This is when you add the ingredients you don't saute, such as grated cheese, freshly chopped herbs and spices.
Chop the primary flavoring ingredients in pieces of the same approximate size. You need about 1 cup of chopped ingredients for a 10-inch frittata.
Saute the primary flavoring ingredients in a scant amount of butter and season them to taste. Fully cook proteins, such as chicken and bacon, before cooking the vegetables. Asparagus, green beans, artichokes, tomatoes and onions work well.
Set aside a small amount of primary flavoring ingredients to use as a garnish. Spread the ingredients in an even layer in the pan and set the heat to low.
Whisk the eggs vigorously once more and gently pour them in the skillet. Cover the skillet.
Cook the frittata covered over low heat until the bottom sets, about 15 minutes. The eggs will be loose on top; garnish the top of the frittata with the reserved ingredients. Heat the oven broiler while the eggs cook on the stove.
Uncover the skillet and set it about 4 inches under the broiler. Broil the frittata just until the top sets, about 4 minutes.