In another bowl, start to whip the egg whites with a hand or stand mixer on low speed. After about 45-60 seconds, add the cream of tartar and make sure that it breaks up throughout the egg whites. Beat on low speed, then very gradually raise the speed. As the egg whites begin to form peaks, slowly add the 1/4 cup of sugar. Continue to gradually raise the speed to high. Beat the egg whites until they form stiff peaks. Fold the whipped egg whites into the chocolate cream mixture, blending gently until the mixture is a uniform color.