Heat 2/3 cup dark brown sugar, 1/3 cup molasses, 4 tablespoons butter, 2 tablespoons water and 1/2 teaspoon each ground ginger, allspice and cinnamon in a saucepan over medium-low heat, stirring, until smooth, about 3 minutes. Let cool slightly. Serve over chocolate chip ice cream with whipped cream, crushed gingersnaps and toasted sliced almonds.