Preheat oven to 400°F. Line a large rimmed baking sheet with aluminum foil and spray with olive oil cooking spray.

In a large mixing bowl, combine ground beef, Italian sausage, egg, breadcrumbs, parmesan, onion, half & half, garlic, Italian seasoning, salt, and black pepper. Mix until just combined.

Use a cookie scoop to portion the meat mixture into 15 balls. Gently flatten each into a disc about 3.5 inches wide.

Place a mozzarella cube in the center of each disc. Fold the meat around the cheese and gently roll into a meatball, ensuring cheese is sealed inside.

Place the stuffed meatballs onto the prepared baking sheet. Repeat with remaining mixture.

Bake for 20-25 minutes or until browned and cooked through. Rest for 5 minutes after baking.

While meatballs are baking, warm marinara sauce in a skillet over medium-low heat.

Serve meatballs with warmed sauce, garnished with chopped parsley and additional parmesan if desired.