Chocolate Cake Roll

JD calls this the homemade version of the Swiss Cake Roll.

6 eggs, seperated
1 c sugar, divided
1 tsp vanilla extract
1/4 c all-purpose flour
1/4 c baking cocoa
1/4 tsp salt
1/2 tsp cream of tartar
1 1/2 c whipping cream
2 tbsp confectioners sugar
Additional confectioners sugar

Place egg whites in a small mixing bowl, let stand at room temp. for 30 minutes. In a large mixing bowl, beat egg yolks on high speed until light and fluffy. Gradually add 1/2 sugar beating until thick and lemon colored. Stir in vanilla. Combine the flour, cocoa, and salt, add to egg yolk mixture until blended.
Beat egg whites on medium until foamy. Add cream of tartar; beat until soft peaks form. Gradually add remaining sugar, 1 tbsp at a time, beating on high until stiff peaks form. Stir a fourth of the egg white mixture into chocolate mixture. Fold in remaining egg white mixture until no egg white streaks remain.
Line a greased 15x10x1 baking pan with parchment paper; grease the paper. Spread batter evenly in pan. Bake at 350 degrees for 12-15 minutes or until cake springs back when lightly touched in center (do not overbake!) Cool for 5 minutes. Invert onto a kitchen towl dusted with confectioners sugar. Gently peel off parchment paper. Roll up cake in the towel, jelly-roll style, starting with the short side. Cool completely on a wire rack.
In a mixing bowl, beat cream and confectioners sugar until stiff peaks form; chill, unroll cake, spread with whipped cream to within 1/2 inch of edges. Roll up again. Place seam side down on serving platter; chill. Dust with additional confectioners sugar before serving.