Preheat oven to 375°F. Grease 10 x 15 inch jelly roll pan with butter and line with parchment paper. Grease and flour the parchment paper. (Very important so cake doesn't stick). In a medium bowl, sift together the flour, cocoa, baking powder and salt. Set aside.
In medium bowl, beat egg yolks until thick, gradually adding 1/3 cup sugar. In another bowl, beat egg whites until foamy, gradually adding 1/3 cup sugar and beat until stiff peaks form. Slowly fold egg whites into yolk mixture, careful not to break the egg whites. Add the flour mixture and mix until incorporated. Spread evenly in pan and bake at 375°F for 8 to 10 minutes. Toothpick should come clean when done. (Keep in mind this is a sponge cake so should be "sponge-like")
Put a dish towel on counter and sift powdered sugar over it until completely covered. Loosen cake from sides of pan and turn onto sugar coated towel. Peel off the parchment paper. Starting at the narrow end, slowly roll up the cake and towel together. Place on rack and allow to completely cool.
Once cake is cook, slowly unroll cake. Spread peppermint bark filling to completely cover the cake. Slowly roll the cake back together, not using the towel this time. (Some of the cake might stick to towel, so just be careful and don't stress if some comes off as you'll be covering with frosting)
Place cake on serving platter. Frost with frosting. (It should be just enough to cover the cake). Use a fork and run through the frosting so it looks like bark. Top with some crushed peppermint and powdered sugar if desired. Enjoy!