Preheat oven to 350 degrees. Line jelly roll pan or cookie sheet with sides with foil, overlapping the ends. Grease and flour foil.
Beat egg yolks and 2/3 cup sugar until thick and tripled in volume. Beat in vanilla. In clean, large bowl beat egg whites until foamy; add remaining 2 tablespoons sugar and pinch of salt. Beat until stiff peaks form.
Fold 1/3 of whites into yolks to lighten. Sift cocoa over top of this mixture and fold in gently. Fold in remaining whites. Spread in prepared pan and bake 15 minutes.
