In large bowl, beat egg whites with cream of tartar until very stiff. Slowly add 3/4 cup sugar. Set aside. In a small bowl, mix together the 3 Tbsp. each of cocoa, sugar, and boiling water; cool for a few minutes. Beat egg yolks until fluffy. Add 1/4 cup water, 3/4 cup sugar, 1 cup flour sifted with 1 tsp. baking powder; then add vanilla. Slowly fold into egg white mixture. Divide in half. Then, fold cocoa mixture into one half of the mixture. Alternate pouring mixtures into a 10-inch angel food cake pan. Cut with knife to remove air bubbles. Bake on bottom rack of oven for 1 hour at 375 degrees. Remove from oven and invert pan.