2 large eggs (or just eggwhites)
1 recipe filling (see below)
Recipe
Place rack in upper third of oven. Heat oven to 350ºF. break eggs into a bowl and lightly beat with fork. Spray 9" ovenproof skillet with nonstick cooking spray. Heat over med high heat. Put filling in pan. Give eggs another stir, then pour into the pan, covering the filling, and stir lightly with a fork until eggs start to set, about 20 seconds. Reduce heat to med low. Once bottom is firm and about 1/2" thick, about 2 minutes, use a spatula to lift the edge of the frittata. Tilt the pan towards that edge so the uncooked egg runs underneath. Lower the edge and swirl the pan gently to distribute the egg evenly. Continue cooking until the egg on top, while still not set, is no longer runny, about 4 minutes.
Place skillet in oven until top is set and just dry to touch, about 2-4 minutes. Check each minutes after two, because frittata will turn tough if cooked too long. Run spatula around edges and underside to loosen the frittata, and then invert or slide onto serving plate. Season with salt and pepper, then serve immediately. To double servings, use 4 large eggs and cook in 12" skillet.
Fillings: For veggies, slice or chop veggies like mushroom, spinach, asparagus, and so on fine, using no more than 2/3 c. for each frittata, and saute them in skillet using drop of oil or cooking spray until they're nearly cooked. (They'll finish cooking after you've added the eggs. You'll get a more satisfying flavor if you include at least 1 tbl. chopped onion or shallots along with veggies of your choice. When veggies are cooked, pour eggs on top and cook as directed in basic recipe.
Herbs: For each single serving frittata, beat about 2 tbl. minced fresh herbs into eggs before pouring them into heated skillet. Or use 1/2 tsp crumbled dry herbs. Try parsley, basil, chives, marjoram, tarragon or oregano.