• Preheat oven to 350 F. Prepare an ungreased 10-inch tube pan. In a medium bowl, combine flour, salt, and baking powder.
•  In the bowl of a stand mixer, whisk the egg whites on medium-high speed until frothy. Add the cream of tartar and continue to whisk until egg whites form soft peaks. Gradually add 1/2 cup sugar while the mixer is running and continue beating until the egg whites form firm peaks that hold its shape when the whisk is lifted.
• Meanwhile, beat the egg yolks in a bowl until it is slightly thicker. Add the sugar and mix until incorporated. Add water, oil and vanilla extract. Mix well.
• Add flour mixture gradually into the yolk mixture and mix until the batter is smooth. Gently fold the egg whites to the yolk batter in three additions until batter is uniform. Pour batter into a prepared 10-inch tube pan. Bake for 60-65 minutes, or until a toothpick inserted in the middle of the cake comes out clean. Invert cake on top of an overturned mug and let cool.
• To unmold cake, loosen sides with a knife. Using your hands, gently push the cake away and downwards from the walls of the pan. Remove the outer ring. Loosen the bottom of the cake with a spatula. Remove gently and invert to a serving plate. 

Make the Mocha Icing

• Melt the butter in the microwave. Stir in the coffee granules and cocoa powder until dissolved. Let the mixture cool down a bit. In a large mixing bowl, combine the butter mixture, icing sugar, and heavy cream. Whisk together until smooth. Add more cream, 1 teaspoon at a time, if the icing turned out too thick for spreading.
• Spread the icing on the cake and garnish with grated chocolate.