The cornstarch is a thickener. Try using sugar free instant pudding mix instead of cornstarch. I am a diabetic. I love peanut butter. The usual ingredients in peanut butter are peanuts and salt .
Some brands add hydrogenated vegetable oil or sugar .
There are several brands of peanut butter available in the refrigerated section of most grocery stores that are really good. They have just peanuts and salt and the oil does not separate out as long as the peanut butter is refrigerated. One tablespoon of peanut butter is exchanged for one meat and one-half fat exchange. Peanuts contain some protein and fat in the form of peanut oil. So when you eat peanut butter at a meal, reduce one meat at that meal.