Start the sauce by cooking the onion in 1/4 cup of the broth in a covered casserole for 4 to 5 minutes or until softened. Stir in the garlic, peppers and paprika and cook for 1 minute, then add the tomatoes, tomato paste, and the remaining broth. Season and simmer, uncovered, for 10 minutes. While the sauce is cooking, mix the meatball ingredients together with seasoning and shape into 24 small balls. Brown the meatballs in 2 batches in a nonstick frying pan, then add to the sauce and simmer for 20 minutes. Cook the spaghetti in a large saucepan of lightly salted boiling water for 7 minutes, then stir in the cabbage and cook for another 5 minutes. Drain and divide the pasta and cabbage between warmed bowls. Spoon the meatballs and sauce over the pasta and top each serving with a teaspoon of sour cream.