Step 1: Preheat your oven to 375°F (190°C).
Step 2: In a large bowl, whisk together the eggs, milk or cream, salt, black pepper, and any desired herbs (like fresh chives or parsley) until well combined but not overly frothy. Set aside.
Step 3: Heat olive oil or butter in an oven-safe, non-stick skillet (10-inch is ideal) over medium heat. Sauté your chosen vegetables (onions, bell peppers, spinach, mushrooms) until tender-crisp. If using cooked meat (like ham or bacon), add it now and warm through.
Step 4: Distribute the sautéed vegetables and any meat evenly across the bottom of the skillet. Sprinkle about half of your grated cheese over the vegetables.
Step 5: Pour the whisked egg mixture evenly over the vegetables and cheese in the skillet. Gently shake the pan to ensure the eggs settle into all the crevices.
Step 6: Cook on the stovetop for 3-5 minutes, or until the edges of the frittata begin to set and pull away from the sides of the pan, but the center is still liquid. This initial stovetop cooking helps create a solid base.
Step 7: Transfer the skillet to the preheated oven. Bake for 12-18 minutes, or until the frittata is puffed, set in the center, and lightly golden brown on top. The exact time will depend on your oven and the thickness of your frittata.
Step 8: Carefully remove the skillet from the oven. Let the frittata rest in the pan for 5 minutes before sliding it onto a cutting board or serving plate. This resting period allows it to set completely and makes it easier to slice.
Step 9: Garnish with extra fresh herbs or a sprinkle of additional cheese, if desired. Slice into wedges and serve warm or at room temperature. Enjoy your delicious homemade frittata!