Preheat the oven to 400°F (200°C). Lightly coat the cavities of a 12-cup muffin pan with nonstick cooking spray.
Remove the crescent roll dough from its packaging without unrolling it. Slice the dough into 12 equal sections.
Press one dough section into each muffin cup, shaping it into a small crust that covers the bottom and sides.
Spoon a little pizza sauce into each dough cup, then sprinkle with shredded mozzarella cheese.
Add the mini pepperoni, keeping the filling within the dough cups so the crust has room to puff up as it bakes.
Bake for 8–10 minutes, or until the crescent roll crusts are golden and the cheese has melted.
Let the mini pizzas cool briefly in the pan before carefully removing them. Serve warm with extra pizza sauce for dipping.