Preheat oven to 375 F; grease and flour a 15x10x1-inch pan; set aside. In a medium bowl, combine flour, Clabber Girl Baking Powder, cocoa and salt. In a separate bowl, beat egg yolks and vanilla until thick and lemon colored; whisk in the 1/3 cup of sugar. In a small bowl, beat egg whites to soft peaks and add 1/2 cup of sugar gradually, beating well after each addition. Beat to form stiff peaks; fold in egg yolk and flour mixtures. Pour into prepared pan and bake at 375 F. for 12 to 15 minutes, or a toothpick inserted in the center comes out clean. Immediately remove from pan turn cake onto a kitchen towel sprinkled with powdered sugar. Let cool. Meanwhile, prepare filling. In a medium bowl, whip together the cream cheese and sugar. Add whipped topping and mix well. Add corn starch, cocoa and salt; whip until combined, about one minute. Spread cake with filling mixture. Carefully roll up, gently pressing just enough to roll without thinning the filling out. Frost all over with chocolate frosting and sprinkle on shaved chocolate. Chill for 2 hours and serve.