• Prehat oven to 350 degrees. Grease 15x10x1-inch baking jelly roll pan. Line bottom of the pan with parchment paper.
• Prepare cake batter as directed on package using water. Add the cocoa and mix until combined. Spoon the batter into the lined jelly roll pan.
• Bake for 17-22 minutes or until golden brown and cracks in cake appear dry. Remove from the cake from the oven.

Rolling the cake:

• Meanwhile, place a clean towel on a flat work surface. With sifter, lightly sprinkle powdered sugar onto the towel.
• While the cake is still warm, loosen the edges with a spatula; immediately invert cake onto the sugared towel. Remove the pan and peel off the parchment paper.
• Starting with long side, roll up the cake in the towel and allow to cool on a wire rack for 45 minutes or until completely cool. You can place it in the refrigerator, too.

Assembling the cake:

• In a large bowl, beat the heavy whipping cream until stiff peaks form. Add the powdered sugar and vanilla and gently combine.
• To assemble the cake, carefully unroll the cooled cake, removing it from the towel. Spread whipped cream evenly over the cake, leaving ½-in border.
• Sprinkle fresh raspberries over the whipped cream. Re-roll the cake, jelly-roll fashion (cake may crack some).
• Place 2 spatulas under the cake roll, and transfer seam side down to a long platter. Store loosely covered in refrigerator at least 1 hour or up to 6 hours.
• To serve, sprinkle cake with sifted powdered sugar and garnish with more fresh raspberries.