Use 1½ ounces of your favorite semisweet chocolate for every cup of base. Although you can simply melt the chocolate in the base, the ice cream will be smoother if you make a chocolate sauce first. Use 1½ tablespoons water for every 1½ ounces of chocolate to make the sauce. Bring the chocolate and water to a boil. Stir until smooth and add to the ice-cream base.