Preheat oven to 360F. Line 12″x 16″ jelly roll pan with parchment paper.
Beat eggs and egg yolk. Add sugar, beating continuously.
Mix for at least five minutes.
Slowly add oil to the egg mixture and then stop mixing.
Sift in flour with cocoa and baking powder.
Manually mix until all ingredients are blended.
Spread the batter in your prepared pan. Bake for 12 minutes.
Cool on a wire rack. There is no need to invert on the towel or roll. Just leave to cool in the pan.
Filling:
Break the chocolate bars into small pieces and put it into a bowl. Add butter.
Over stovetop, heat the whipping cream to close to a boiling point. Pour over the chocolate and mix with a wire whisk until chocolate is melted.
Cool completely and refrigerate for at least 2 hours.
Once cooled start beating on medium and then beat on high. Mix until the filling is creamy and easy to spread. Be careful not to over-mix.
Spread about two-thirds of the filling onto the cake, the rest will be saved for the outside of the roll. As you roll the cake pull off the parchment paper. Cover the cake with the rest of the chocolate filling. Cool well and decorate with chocolate glaze or whipped cream icing.