In a small bowl, sift together 1/2 cup sugar, flour, cocoa, and espresso granules; set aside. In a large bowl, beat egg whites until foamy. Add cream of tartar and salt; beat until soft peaks form. Add remaining 3/4 cup sugar, 2 tablespoons at a time, beating until stiff peaks form. Sift flour mixture over egg white mixture, 1/4 cup at a time; fold in after each addition. Fold in vanilla extract.
Pour batter into an ungreased 10" tube pan, spreading evenly. Break large air pockets by cutting through batter with a knife. Bake at 375° F for 35 minutes or until cake springs back when lightly touched. Invert pan; cool completely. Loosen cake from side of pan using a narrow metal spatula; remove from pan. Sprinkle cake with powdered sugar.