Preheat oven to 350.
Prepare the cake according to package directions, adding the 3 tablespoons of cocoa to the mixture. Coat a 15 X 10 inch jelly roll pan with cooking spray. Line the bottom of the pan with wax paper or parchment. Pour batter into the pan.
Bake @ 350 for 25 minutes or until cake springs back when touched lightly in the middle. Cool cake for 5 minutes in pan. Loosen cake from sides of pan and turn out onto a clean kitchen towel sprinkled with 1/2 cup of confectioners sugar. Carefully peel off the wax paper. Let cool another minute. Starting at the narrow end, roll up the cake and towel together. Place seam side down on a wire rack and cool completely; about 15 - 20 minutes.
Meanwhile, prepare the filling. Place chocolate in a glass bowl and microwave at 50% power for about 2-3 minutes. Stir halfway and continue microwaving and stirring until all melted. Set aside. Place the cream cheese in a large bowl and cream until smooth. Gradually add the melted chocolate and 1 cup confectioners sugar. Beat mixture well until smooth. It will be very thick. Add the whipped cream and fold into the mixture.
Carefully unroll the cake. Spread the filling over the cake leaving a 1/2 inch border around the edges. Re-roll the cake without the towel. Place seam side down on a platter. Remove the edges of the cake roll as they are sort of crispy. Cover the cake roll with plastic wrap and chill for 30 minutes. To serve, unwrap cake roll, garnish with a sprinkle of dark cocoa or chocolate curls. Cut into 10 pieces.