1. Combine sugar and cornstarch in a deep, 1-quart, heat- resistant non-metallic casserole. 2. Gradually add water, stirring constantly. 3. Add butter and heat, uncovered, in Microwave Oven 5 minutes; stir every 1 1/2 minutes. 4. Heat, uncovered, in Microwave Oven an additional 3 minutes or until sauce is thickened and clear. Makes 2 cups