If like me you will be reheating these the next day you may want to reduce the cooking time to 10 minutes if it is thickening too quickly. I found 15 minutes was perfect. If you find when you go to reheat (on a low heat) that the mixture has thickened too much and is in danger of burning while you're reheating just add a little water at a time until it loosens a little. You don't want it too runny though or it wont coat the meatballs properly.