Whisk together flour, baking powder, and salt in a bowl.
Cream the butter and sugar in a separate bowl. Beat in the egg.
Add the dry ingredients into the wet mixture. Knead into a smooth dough. Wrap in clingfilm and refrigerate for an hour.
Put the dough on a lightly floured surface and roll out to about ¼” thick.
Cut the dough with a round biscuit cutter.
Take a piece of dough and fill with a small dollop of marinara, a slice of pepperoni, and a cube of mozzarella.
Bring the edges of the dough together and press together to seal into a ball.
Mix together the butter and Italian seasoning.
Brush the balls with butter mixture.
Arrange on a parchment-lined baking sheet and bake for 15 minutes at 375F.