Slow Cooker Mozzarella Stuffed Meatballs

Name: Slow Cooker Mozzarella Stuffed Meatballs
Prep time: 5 min
Cook time: 2 h 40 min
Total time: 2 h 45 min
Cuisine: European, Italian, Mediterranean
Ingredients: 1 pound lean ground beef; 1 pound mild Italian sausage; 1 cup breadcrumbs; 1 small yellow onion, finely chopped; 3 cloves garlic, minced; 1/4 cup Parmesan cheese, grated; 2 whole eggs; 1/2 cup whole milk; 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)