Since some sweeteners are sweeter than others, and some berry combinations are more tart, start with a ½ cup. After it has been cooking for about 10 minutes, taste to see if you need to add a little more before it finishes cooking. If your frozen berries contains large strawberries, you may want to mash them with a potato masher before it’s done cooking. This is also delicious as a topping on french toast, pancakes, oatmeal, ice cream, and cheesecake.