Preheat the oven to 400°F. Line a large rimmed baking sheet with aluminum foil and spray it with olive oil cooking spray. Set aside.
In a large mixing bowl, combine the lean ground beef, mild Italian sausage, egg, breadcrumbs, grated parmesan cheese, finely minced yellow onion, half & half, grated garlic, Italian seasoning blend, salt, and black pepper. Mix until well combined, being careful not to overmix.
Use a 2-inch-sized cookie scoop to portion out 15 meatballs. Flatten each meatball into a disc, then place a mozzarella cheese cube in the center. Carefully fold the sides up and around the cheese cube, shaping the mixture into a meatball.
Arrange the stuffed meatballs on the prepared baking sheet in rows.
Bake the meatballs for 20-25 minutes, or until lightly browned and cooked through.
While the meatballs are baking, warm the marinara sauce in a medium skillet over medium-low heat.
Once the meatballs are cooked, remove them from the oven and let them rest for five minutes.
To serve, spoon some warm marinara sauce onto a serving plate, add the meatballs, and spoon additional sauce over the top. Garnish with grated parmesan cheese and fresh chopped parsley.
Enjoy these delicious Cheese Stuffed Meatballs as a satisfying main course!