Preheat the oven to 350°F and lightly coat a 13×9-inch metal cake pan with cooking spray.
Add the cake mix to a large bowl and break up any clumps.
In a medium bowl, whisk 1 cup cold water, the vegetable oil, and eggs until well combined.
Pour the wet ingredients into the cake mix and beat with a hand mixer on medium speed for 2 minutes, scraping the bowl halfway through.
Spread the batter evenly in the prepared pan and bake for 22 to 25 minutes, until a toothpick comes out clean.
Cool the cake on a wire rack for 30 minutes, then poke holes all over the surface about 1 inch apart using a skewer.
Whisk the raspberry gelatin into 1 cup boiling water for about 2 minutes until dissolved, then stir in the remaining 1 cup cold water.
Slowly pour the gelatin mixture over the cake, cover tightly, and refrigerate for 6 to 12 hours.
Place the white chocolate chips in a bowl. Heat 1/2 cup of the heavy cream until steaming, then pour over the chocolate.
Let sit for 2 minutes, then whisk until smooth. Cover with plastic wrap touching the surface and chill for 6 to 12 hours.
In a stand mixer, whip the chilled white-chocolate mixture with the remaining 1 cup heavy cream and vanilla until stiff peaks form, 2 to 4 minutes.
Spread the whipped topping over the chilled cake and garnish with fresh raspberries before serving.