1/2 cup fresh parsley, finely chopped, plus more for serving
1/2 teaspoon kosher salt
1/2 teaspoon pepper
6 sticks mozzarella cheese, cut into 4 pieces each
6-8 cups marinara sauce, homemade or store bought
Kaiser rolls and provolone cheese for serving (optional)
01Preheat oven to 425 F. Line rimmed baking sheet with parchment paper. Combine beef, sausage, breadcrumbs, onion, garlic, Parmesan, eggs, milk, parsley, salt and pepper in large mixing bowl. Mix together with hands until just combined.
02Shape about 1/4 cup meat mixture into ball and push mozzarella cheese piece into center, rolling into ball shape to seal in cheese. Repeat with remaining meat and cheese. Arrange meatballs on prepared baking sheet and bake 10 minutes, until tops are browned.
03Coat bottom of slow cooker with 1 cup marinara sauce. Add enough meatballs to cover sauce in one layer, and top with 2 cups of marinara sauce. Continue layering meatballs and marinara until all are used. Cover and cook 2 1/2 hours on high, until meatballs are cooked through. Top with fresh parsley and keep warm until serving. Serve as appetizer or on kaiser rolls with provolone cheese.