Preheat oven 350º
To prepare the cake, combine 3 T cocoa and cake mix in a lg bowl. Prepare mix according to directions. Coat 15x10 jelly roll pan with cooking spray and line with waxed paper (important)
Pour batter into pan.
Bake 350º for 25 min. or until cake springs back when touched lightly.
Cool cake in pan 5 min. Loosen cake with a spatula, turn onto a dish towell dusted with 1/2 cup powdered sugar, carefully peel off waax paper.
Cool the cake 1 min. Starting at narrow end, roll cake and towell together. Place seam side down onto a wire rack and cool completely, about 15 min.
To prepare the filling, place baking chocolate in a glass bowl and microwave on high 2 min. or until almost melted, stirring after 1 min. Cool, place cream cheese in a med bowl and beat with a mixer at med. speed until smooth. Gradually add melted chocolate and 1 cup powdered sugar, beating mixture well. Gently stir half whipped topping into filling and gently fold in remaining whipped topping.
Carefully unroll cake, remove towell. Spread filling over the cake, leaving 1/2 in. border around the outside edge. Refoll cake, and place, seam side down on a platter. Cover and chill for 30 min. Sprinkle with 1 tsp cocoa. Cut the cake into 10 slices, garnish with chocolate curls.