1 cup cake flour, sifted
3 tablespoons instant espresso powder
12 egg whites
1/4 teaspoon salt
1 teaspoon cream of tartar
1 1/3 cups granulated sugar
1 cup Nutella
1/2 cup confectioners' sugar
6 tablespoons boiling water

Preheat oven to 350 degrees F.

In small bowl, stir together cake flour and espresso powder.

In large bowl, using electric mixer on medium speed, beat egg whites, salt and cream of tartar until frothy (about 1 minute). Increase speed to high, beating until soft peaks form. While continuing to mix, gradually add sugar (1 tablespoon at a time). Beat until sugar has dissolved and mixture holds firm peaks when beaters are raised. (Do not over-beat.)

Sprinkle 1/3 flour mixture over batter and gently fold in using rubber spatula. Before completely incorporated, add 1/3 more flour mixture and continue to fold. Add remaining flour and fold batter together completely. (Do not over-mix. Over mixing will cause cake to become flat.)

Place mixture into ungreased 10-inch tube pan and bake for 45 to 50 minutes. Remove pan from oven and immediately turn cake upside down onto cooling rack. (Do not remove cake from pan at this time.)

When cake has completely cooled, run knife around outer edge and center to loosen. Invert onto cake plate and carefully lift off outer pan. Run knife along top part of cake and remove tube insert.

Meanwhile, in medium bowl, whisk together Nutella, confectioners' sugar and boiling water until smooth. Drizzle over top of cake and serve.