1. Preheat the oven to 375 degrees. Grease a 24-cup mini-muffin pan. In a large bowl, whisk together the flour, baking powder, Italian seasoning, salt and red pepper flakes (if using) ; whisk in the milk and egg. Stir in the mozzarella, Parmesan and pepperoni; let stand for 10 minutes.
2. Stir the batter and divide among the mini-muffin cups. Bake until puffed and golden, 20 to 25 minutes.
3. Meanwhile, microwave the pizza sauce until warmed through. Serve the puffs with the pizza sauce for dipping.
NOTE: All my batter did not fit into the 24-mini muffin pan. So I made a full size muffin with the leftover batter. Some pans are larger than others so you may not have have an issue.