1

Preheat oven to 375°F. Line bottom of 9-inch springform pan with wax paper; spray with nonstick spray.

2

Whisk together 1/2 cup of granulated sugar, 1/4 cup of cocoa, the chocolate, butter, espresso powder, and salt in medium bowl. Add boiling water and stir until chocolate is melted and mixture is smooth; let cool slightly. Whisk egg yolks into chocolate mixture until smooth. Gradually add flour, stirring just until blended.

3

With electric mixer on medium speed, beat egg whites and cream of tartar in large bowl until soft peaks form when beaters are lifted. Add remaining 1/4 cup granulated sugar, 1 tablespoon at a time, beating until stiff, glossy peaks form when beaters are lifted.

4

With rubber spatula, stir one-fourth of beaten egg whites into chocolate mixture to lighten it, then gently fold in remaining whites just until no streaks of white remain. Scrape batter into prepared pan.

5

Bake until toothpick inserted into center of cake comes out with moist crumbs clinging, about 35 minutes. Let cool completely in pan on wire rack (cake will sink slightly in center). Run thin knife around side of cake to loosen from pan; release and remove side of pan. Just before serving, dust top of cake with remaining 1 tablespoon cocoa.