Preheat oven to 325 F. Beat egg yolks till thick and lemon colored; add water and continue beating until very thick. Add sugar and vanilla. Sift together flour, cocoa and salt in separate bowl. Fold flour mixture into egg yolk mixture. Beat egg whites until foamy; add cream of tartar and beat until whites form moist, glossy peaks. Fold whites into first mixture. Bake in ungreased (10-inch) round tube pan 1 hour. Invert to cool. Cut cake horizontally into 3 layers. Cover first layer with mocha filling and 2nd layer with white glaze (see recipes below). Spread top and sides with chocolate mixture (below). Drizzle white glaze around edge of top and down sides. Serve immediately or chill in refrigerator before serving. Mocha Filling And White Glaze: Melt 1 cup butter in saucepan over medium heat. Add 2/3 cup sugar, 2/3 cup flour and 1/2 tsp. Salt. Turn heat to medium-high; add 4 cups milk and 3 tsps. Vanilla and stir continuously until mixture thickens and starts to bubble. Remove from heat and pour about half into separate bowl. Add 4 ozs. German sweet chocolate, cut into chunks, to mixture in saucepan, and stir until melted. Cool until just warm before frosting cake.