Step 1: Prepare the Pickle-Brined Cream (Optional, but Recommended). In a small bowl, combine the dill pickle brine, with the reserved heavy cream. Let sit.

Step 2: Preheat Oven and Prepare Pan. For the cake: Preheat the oven to 350°F (175°C). Spray a 13×9-inch cake pan with cooking spray.

Step 3: Mix Cake Batter. Place the cake mix in a large mixing bowl. In a medium mixing bowl, whisk together 1 cup of cold water, oil, and eggs. Add the wet ingredients to the cake mix, whisking until well combined.

Step 4: Bake the Cake. Pour the batter into the prepared baking dish. Bake according to package directions, 22 to 25 minutes.

Step 5: Cool the Cake. Let the cake cool in the pan for 30 minutes on a wire rack.

Step 6: Prepare the Jello Mixture. While the cake is cooling, prepare the Jello mixture. In a medium bowl, dissolve the raspberry gelatin in 1 cup of boiling water. Once all of the gelatin is dissolved, stir in the remaining 1 cup of cold water.

Step 7: Poke and Infuse. Prick the cooled cake all over with a toothpick. Pour the prepared gelatin mixture evenly over the cake.

Step 8: Chill. Cover the cake and refrigerate for at least 6 and up to 12 hours.

Step 9: Make the White Chocolate Base. For the white chocolate whipped cream: Place the white chocolate chips in a medium heatproof bowl. Pour ½ cup of the regular (non-brined) heavy cream into a microwave-safe measuring cup. Microwave until the cream is steaming, 30 seconds to 1 minute; do not let it boil.

Step 10: Melt Chocolate. Pour the hot cream over the white chocolate and allow to sit for 2 minutes. Whisk the chocolate and cream until well combined.

Step 11: Chill Chocolate Mixture. Cover the bowl with plastic wrap and refrigerate until chilled, at least 6 and up to 12 hours.

Step 12: Whip Remaining Cream. In the bowl of a stand mixer fitted with the whisk attachment, combine the remaining (non-brined) 1 cup of heavy cream and vanilla. Beat on medium-high speed until stiff peaks form, 2 to 4 minutes, scraping the bottom and sides of the bowl occasionally.

Step 13: Combine Whipped Cream and Chocolate. Add the chilled white chocolate mixture and the dill pickle powder to whipped cream. Beat again until combined.

Step 14: Whip Brined Cream (Separately). In a separate bowl, whip the pickle-brined cream until soft peaks form. Do not over-whip.

Step 15: Frost and Garnish. Spread the white chocolate whipped cream (the main batch, not the pickle-brined whipped cream) onto the chilled cake.

Step 16: Serve. Serve cold with fresh raspberries. Dollop small spoonfuls of the pickle-brined whipped cream around the edges of the cake, or offer it on the side, as a separate topping. Offer dill pickle relish on the side, if desired.