The cake can be made a day in advance. Store wrapped in plastic wrap at room temperature.
Espresso Chocolate Chip Angel Food Cake
Makes a 10-inch cake
2 teaspoons instant espresso powder
1 1/3 cups cake flour, sifted
1/8 teaspoon kosher salt
1 3/4 cups (about 12 large) egg whites
1 teaspoon cream of tartar
1 3/4 cups granulated sugar
1 1/2 teaspoons vanilla extract
1 1/4 teaspoons freshly squeezed lemon juice
3/4 cup chocolate chips, coarsely choppe
Preheat the oven to 350°.
Sift together the espresso powder and the cake flour. Stir in the salt. Put the egg whites in the bowl of an electric mixer. Using the whisk attachment, whip the egg whites on medium speed until frothy. Add the cream of tartar. Increase to high speed and slowly pour in the sugar. Continue whipping until the whites are firm and satiny, about 3 minutes.
Reduce to low speed and add the vanilla extract and lemon juice. Add the reserved flour mixture. When the flour mixture is almost completely incorporated, remove the bowl from the machine and fold in the chocolate chips. Make sure that the chocolate chips are spread throughout the batter and that the flour is evenly mixed into the egg whites. Do not over-mix. Pour the batter into an un-greased 9 1/2-inch angel food cake pan. Cut through the batter a few times with a table knife to break up any air pockets. Bake until a skewer inserted in the middle comes out clean, 40 to 45 minutes. Invert the cake on a rack and let cool upside down in the pan.
Unmold the cake and slice it with a serrated knife.