• Preheat the oven to 350°F. Line the bottom of a 10x15x1″ rimmed baking sheet with parchment paper that’s been cut to lay flat. Do not grease the pan.
• Prepare the cake mix according to the package directions. Pour the batter into the prepared pan.
• Bake for about 20 minutes, until the top is golden and the edges start to crack. It will rise up in the pan significantly, possibly over the top, but it should not flow over. (If you’re concerned, slip an extra baking sheet or a piece of foil underneath.)
• While the cake is still warm, use a knife to loosen it from the edges of the pan. (It’s going to be a little sticky, but it will come away easily.)
• Spread out a clean, lint-free kitchen towel and sprinkle it evenly with ¼ cup powdered sugar. Flip the warm cake out onto the towel, peel off the parchment paper, and immediately roll it up, starting at the short end, with the towel inside. Let the cake cool completely at room temperature for 1 to 2 hours or in the fridge for about 1 hour (if you’re impatient like me!).

Cream Cheese Filling

• In a large bowl, beat the cream cheese with an electric mixer, until smooth. Add the powdered sugar, cream, and vanilla and beat on low, until combined, then on high for a few minutes, until fluffy and thick. Be careful not to overmix or it may become thin again.
• Unroll the cooled cake. (You can leave it lying on the towel.) Spread the cake with half of the filling and top with half of the strawberries, blueberries, and raspberries. Carefully roll the cake back up (this time without the towel!) and place on a serving plate.
• Spread the top and sides with the remaining filling and top with remaining berries. Serve.