Preheat the oven to 375°F. Grease a 24-cup mini-muffin pan with cooking spray, and set aside.
In a large mixing bowl, whisk together the flour, baking powder, Italian seasoning, and salt. Whisk in the milk and egg. Stir in the mozzarella, Parmesan and pepperoni. Let sit on the counter for 10 minutes to help the flavors meld together.
Stir the batter and portion into the mini-muffin cups. Bake for about 20-25 minutes- until puffy and golden.
Remove from oven and serve with warmed pizza sauce.
Adapted from Rachael Ray