Preheat your oven to 375°F (190°C). Lightly grease your muffin tin with cooking spray or use silicone liners for easy release. This prevents sticking and ensures easy cleanup.
Crack the eggs into a large mixing bowl. Add the milk, salt, and pepper, then whisk until fully combined and slightly frothy. This creates a light texture and helps the muffins rise a bit during baking.
Chop your veggies, meats, and herbs as needed. Try to keep pieces small and even for uniform cooking. If using frozen spinach, make sure to squeeze out excess moisture to avoid soggy muffins.
Evenly divide the chopped vegetables, cheese, and meats into each muffin cup. Then pour the egg mixture on top, filling each cup about ¾ full. Stir each cup gently with a fork to distribute the fillings evenly.
Place the muffin tin in the oven and bake for 18–22 minutes, or until the tops are puffed and a toothpick inserted comes out clean. Avoid overbaking, which can cause the muffins to dry out or become rubbery.
Let the egg muffins cool in the tin for 5 minutes, then use a spoon to gently remove them. Serve warm or let them cool completely before storing. They’ll deflate slightly as they cool — that’s normal!