In 2-quart saucepan combine Sugar, Brown Sugar and butter. Cook over low heat, stirring occasionally, until butter is melted (6-8 min). In large Mixing bowl, combine cooked Mixture with Ice Cream, beat at medium speed, scraping bowl often until smooth (1-2 min). Store refrigerated up to 2 weeks or frozen up to one month. For each serving, fill mug with 1/4 Collins Glass Mixture, 1 oz. Rum and 3/4 Collins Glass boiling Water, sprinkle with Nutmeg.