In a large saucepan saute the onion and garlic in the olive oil. Add ground beef and continue cooking. Stir in prosciutto and cook for 5 to 6 minutes. Add 2 tablespoons of the butter, chopped tomatoes, and tomato paste. Let sauce simmer for 10 minutes. Season with salt and pepper.
Simmer for one hour. Add additional butter and simmer for an additional half hour.
