Preheat your oven to the recommended temperature, usually around 375°F (190°C), and prepare a muffin pan by greasing each cup with cooking spray or lining them with muffin liners.
In a mixing bowl, crack and whisk together the desired number of eggs, typically around 6-8 for a standard muffin pan.
Add in your choice of fillings such as chopped vegetables, cooked meats like ham or sausage, grated cheese, and herbs or spices for flavor.
Pour the egg mixture into each cup of the prepared muffin pan, filling them about three-quarters full to allow for rising during baking.
Bake the frittatas in the preheated oven for approximately 15-20 minutes or until they are set in the center and lightly golden on top.
Remove the muffin pan from the oven and let the frittatas cool slightly before carefully removing them from the pan.