Beat egg yolks until thick and lemon-colored. Sift 1 c. confectioners sugar, flour, salt and cocoa together 3 times; beat into egg yolks until well blended. Add vanilla; fold in egg whites.
Bake in greased and paper-lined 15½ x 10½ x 1" jelly roll pan in moderate oven (375°) 15 to 20 minutes. Lightly dust clean dish towel with confectioners sugar; loosen cake aro