Spray a 24-count muffin tin (or two 12-count muffin tins) really well using non-stick cooking spray. Get the inside and sides of them really good so they don't stick.
Chop the pepperoni into smaller bite-sized pieces.
In a bowl, mix together flour, baking powder, Italian seasoning and salt.
Stir in milk and beaten egg.
Add in shredded cheese and diced pepperoni and crushed red pepper (about ½ teaspoon), if using.
Let mixture sit for about 10 minutes.
Spoon mixture into muffin tins. I like to use a spring-release cookie scoop but spoons work just fine.
Bake for about 20-25 minutes (until golden brown.) Serve with marinara suace, for dipping.
You can also spice it up a bit and add in some red pepper flakes (about ½ teaspoon.)
You can also add in cooked and crumbled sausage. Or even diced green or red peppers.
I recommend using a good quality Italian seasoning. Some store brand seasonings can have an overwhelming amount of oregano rather than an even blend and this can really throw off the flavor of these pizza puffs.