Chocolate Chip Angel Food Cake

I. INGREDIENTS

1. 3 ounces bittersweet or semisweet chocolate, coarsely chopped
2. 1 cup cake flour
3. 1 1/2 cups granulated sugar
4. 13 large egg whites
5. 1 teaspoon cream of tartar
6. 1/4 teaspoon salt
7. 1 1/2 teaspoons pure vanilla extract
8. 1 cup granulated sugar, plus
9. 2 tablespoons granulated sugar
10. 3 large egg whites
11. 1/2 teaspoon cream of tartar
12. Pinch of salt
13. 3 teaspoons pure vanilla extract

II COOKING DIRECTIONS

1. Position a rack in the lower third of the oven and preheat the oven to 375 degrees F. Pulse the chocolate in a food processor until finely ground; reserve. In a medium bowl, whisk together the flour and 3/4 cup of the sugar until combined; reserve.
2. In the bowl of a mixer fitted with a whisk, mix the egg whites, cream of tartar and salt on low speed until frothy, about 1 minute. Increase the speed to medium and beat the egg whites until they hold soft peaks, about 2 minutes. Stir in the remaining 3/4 cup of sugar, then beat the egg whites at medium-high speed until fluffy and just stiff.
3. Remove the bowl from the mixer, sift one-third of the flour mixture over the egg whites and fold it in with a large spatula until just blended. Add the vanilla and fold in the remaining flour in 2 batches. Fold in the reserved ground chocolate and scrape the batter into a 10-inch tube pan. Bake until a toothpick inserted in the center comes out clean, about 45 minutes. Invert the pan and place the tube opening over the neck of a bottle to suspend the cake, then let cool completely, at least 1 hour and up to overnight.
4. Unmold the Chocolate Chip Angel Food Cake and coat generously with the Seven-Minute Frosting.
5. Seven-Minute Frosting: In a large saucepan, bring 1 inch of water to a simmer. In a large stainless-steel bowl, combine the sugar, egg whites, 1/4 cup of water, the cream of tartar and the salt. Set the bowl over the simmering water and beat the egg whites with a whisk or handheld mixer until the frosting holds stiff peaks, about 5 minutes.
6. Remove the bowl and continue to beat until cooled and billowy, about 2 minutes more. Beat in the vanilla and frost the cake.