cream of tartar and salt. Increase speed to medium. Beat until whites are whipped and hold their shape but are still soft and moist. Add 3/4 cup sifted sugar, 1 tablespoon at a time, beating well after each addition, until all sugar is added. Add vanilla. Stop beating when whites have increased in volume about fivefold, hold their shape and are shiny and smooth. Gently but thoroughly fold in flour mixture, by thirds. Transfer to baking pan. Smooth surface with spatula. Cut through batter in 6 places to break any large air pockets. Bake until toothpick inserted in center comes out clean, about 35-to-40 minutes, laying piece of foil lightly over top if it gets too brown. Invert and rest tube on inverted custard cup. Prop pan extensions with crumpled foil to secure pan. Cool completely. When cake is completely cool, use flexible knife to loosen it from sides of pan. Invert onto rack. Keep cake at room temperature 2 days, well covered, or frozen (airtight) as long as 3 months. Be sure to thaw at room temperature in wrapping. Frost. CAPPUCCINO FLUFF FROSTING: Put egg whites, sugar and corn syrup in top of double boiler. Place over simmering water. Immediately use mixer at medium speed to beat ingredients until fluffy, white and warmed through, about 5 minutes. Stir in marshmallows. Once combined, beat at lowest speed until marshmallows are melted and mixture is smooth. Remove from heat. Stir in vanilla, cocoa, espresso and salt. Spread on top and sides of cake. Yield: frosting for 1 10-inch tube cake.