Mix the Dough: In a large mixing bowl, combine sourdough discard, all-purpose flour, baking powder, olive oil, and salt. Stir until a shaggy dough forms.

Rest the Dough: Cover with a towel and let rest for 10 minutes.

Shape the Bombs: Divide the dough into 12 portions, flatten each into a 3-inch circle.

Fill and Seal: Place a mozzarella cube and filling in the center, fold edges over and seal tightly.

Bake: Arrange on a baking tray, preheat oven to 375°F and bake for 18-20 minutes.

Cool and Serve: Allow to cool for 5 minutes before serving with marinara sauce.