My best friend served these whenever we had unexpected guests. Just 2 ingredients.

For a slightly different flavor profile, swap mozzarella for shredded Parmesan or Asiago; both brown beautifully and will give you an even sharper, nuttier crunch.
If your pepperoni is very thin, stack two slices before adding cheese for a heartier bite that still crisps well. To control salt and fat, look for turkey pepperoni or reduced-sodium varieties—they’ll still crisp but may need an extra minute or two in the oven.

You can also play with shapes: cut larger pepperoni slices into halves or quarters before baking for bite-sized pieces that stretch further for a crowd. If you prefer them extra crisp, place the baked crisps briefly on a wire rack set over a tray to drain and dry out more.

Leftovers store well in an airtight container at room temperature for a day; re-crisp them in a low oven (300°F/150°C) for a few minutes before serving.