Preheat the oven to 400°F. Line a large baking sheet with foil and spray with nonstick spray.
In a food processor, pulse pepperoni until it completely ground. Transfer to a large bowl. Add the mushrooms, onion, and garlic to the food processor and pulse until finely chopped.
In the bowl with the pepperoni, add the mushroom mixture, ground beef, eggs, milk, panko, Italian seasoning, paprika, salt, and pepper. Using your hands, mix together until just combined, being careful not to overmix.
Using a medium cookie scoop or a spoon, portion the mixture onto the baking sheet. Using your hands, shape each portion into 1 1/2-inch balls. Return to the baking sheet.
Bake uncovered, turning halfway through, 17 to 20 minutes, or until no longer pink in the center.
Serve with pasta and marinara!
Notes
Important Reminder: Make sure to remove the fresh silica gel packet from the bag before adding pepperoni to food processor. Quantity: Makes 24 to 30 medium-sized meatballs.Storage: These meatballs can be kept in the fridge up to 1 week in an airtight container.Freeze: Store in a freezer-friendly bag up to 3 months. To avoid having them freeze in a clump, flash freeze them on the baking tray first before transferring them to the bag.