Wash and hull strawberries; arrange in a single layer on a sheet of foil and place uncovered in the coldest part of the freezer. When strawberries are frozen solid, remove and put in food processor, using the steel blade. Add 4 tablespoons (50 ml) yogurt and process until soft-serve frozen yogurt forms (add more yogurt for a softer dessert). Sweeten to taste, if desired. Serve immediately. Makes 4 servings, approximately 45 calories each.