Here's your basic frittata recipe:
First, preheat your oven to 350°F. Heat 3 tablespoons of olive oil in a a 10" oven-safe skillet over medium-high heat. Add ½ cup diced onions. Cook, stirring occasionally, until softened, about 5 minutes. Meanwhile, whisk 8 large eggs in a medium bowl with ½ cup of milk, ¾ teaspoon salt, and ¼ teaspoon pepper. To customize, choose one of the additions below.
Pour the egg mixture and any additions into your skillet, stir, and cook just until edges start to pull away from the pan. This will take 5 to 7 minutes. Transfer skillet to oven and bake until set, 16 to 18 minutes. Then enjoy!
For a Lyon frittata:
Add ½ cup each sautéed diced red bell pepper and zucchini, along with ¼ cup finely chopped fresh basil leaves.
For a Cobb frittata:
Add 1 cup each halved cherry tomatoes, diced avocado, and cooked chicken, plus ¼ cup each crumbled cooked bacon and blue cheese.
For an Italian frittata:
Add 8 ounces Italian sausage that you've crumbled and browned, plus ½ cup cooked broccoli rabe, cut into 2-inch segments, and ¼ cup grated Parmesan.
For a spring frittata:
Add 2 cups sliced cooked asparagus, 4 ounces smoked salmon (chopped), and ¼ cup each chopped fresh chives and flat-leaf parsley.
For a Greek frittata:
Add 1 pound baby spinach that you've cooked just until wilted and squeezed dry, plus ½ cup crumbled feta, as well as 2 tablespoons each chopped fresh dill and sliced scallions.
For a corned beef hash frittata:
Add 3 cups diced, cooked potatoes and 8 ounces chopped cooked corned beef.