This heavenly angel food cake is studded with mini chocolate chips and perfumed with fragrant espresso powder. The dessert feels indulgent, but fear not—this homemade version has much less fat than the store-bought kind.
Preheat oven to 350 degrees. In a small bowl, stir together espresso powder, vanilla, and 1 tablespoon water until powder dissolves.
In a large, wide bowl, using an electric mixer, beat egg whites on medium-high until foamy, about 1 minute. Add cream of tartar and beat until soft peaks form, 4 minutes. Continue to beat, gradually adding sugar, until stiff glossy peaks form, about 2 minutes. (If using a stand mixer, gently transfer egg-white mixture to a large, wide bowl for easier folding.)
Place cake flour and salt in a fine-mesh sieve and sift over egg-white mixture in 3 additions, gently folding with a rubber spatula after each addition. Gently fold in espresso mixture and chocolate chips. Gently spoon batter into an ungreased angel-food cake pan with a removable bottom. With a knife, cut through batter to release air bubbles, then smooth top. Bake until cake is golden brown and springs back when lightly pressed, 30 to 35 minutes.
Invert pan on a baking sheet; let cake cool in pan, 1 hour. Run a thin knife around pan and tube, then unmold cake. Serve drizzled with ganache.