Meatball and Pasta Soup

INGREDIENTS

• For the meatballs:
• 1/2 pound lean ground beef
• 1/2 pound bulk Italian sausage
• 1/3 cup grated Parmesan cheese
• 1/3 cup seasoned bread crumbs
• 1/4 cup milk
• 1 egg
• 2 tablespoons dried parsley
• 1 clove garlic, minced
• 1/8 teaspoon ground black pepper
• 2 tablespoons minced onion
• 1 tablespoon olive oil, or as needed
• For the soup:
• 1 tablespoon butter
• 1 large carrot, chopped
• 2 stalks celery, chopped
• 3/4 cup chopped yellow onion
• 7 cups beef stock
• 2 tablespoons Italian-style tomato paste
• 1 (14.5 ounce) can chopped tomatoes
• 1/2 teaspoon salt, or to taste
• 1/4 teaspoon ground black pepper, or to taste
• 6 ounces uncooked tri-color wagon wheel pasta