Meatball Sub Soup

Make the meatballs: Preheat oven to 350 degrees F and line two baking sheet with parchment paper. Make meatballs: In a large bowl, combine ground beef, bread crumbs, garlic, parsley, and crushed red pepper flakes and season with salt and pepper. Roll into meatballs and transfer to one prepared baking sheet. Bake until browned and cooked through, 15 minutes. Heat broiler. Make the soup: In a large pot over medium-high heat, heat oil. Add onion and cook until soft and golden, 6 minutes. Add garlic and cook until fragrant, 1 minute. Add tomatoes, chicken broth, and milk and stir until combined. Add the meatballs and bring to a simmer, then add half the mozzarella and Parmesan. Season with oregano, salt, and pepper. Ladle soup into four oven-safe ramekins and top with a baguette slice. Top with remaining mozzarella and broil until browned and bubbly, 2 to 3 minutes. Serve hot.