Preheat oven to 350º. Line 15x10 jelly roll pan with waxed paper. Grease and flour lined pan; tap out excess.
In a medium bowl, combine flour, cocoa powder, cornstarch, baking soda and powder and salt. Mix well. In a separate bowl beat egg yolks and 1/4 c. sugar until fluffy.
In a small bowl, beat egg whites on high until foamy (be sure to use clean beaters). Gradually add 1/2 c. sugar, beating until stiff, but not dry, peaks form.
Fold 1/3 beaten egg whites into egg yolk mixture. Alternately fold in remaining whites and flour mixture. Pour batter in pan; smooth top. Bake about 15 mins.
Roll & Fill cake
Dust a clean cloth/dish towel with remaining sugar. Turn cake out onto prepared cloth; remove waxed paper. Slightly trim cake edges.
Starting with long side, tightly roll up cake with the cloth inside. Transfer cake, seamside down, to a wire rack to COOL.
Unroll cake; remove cloth. Spread whipped topping over cake to within 1/2" of edges. Re-roll cake; place seamside down on a plate. Dust with confectioners' sugar before serving.