Preheat your oven to 350 degrees F. Grab a baking sheet that measures 13x18x1 and lightly coat it with non-stick baking spray. This will ensure that your cake comes out of the pan easily.
In a large mixing bowl, combine the Vanilla Cake Mix, INSTANT Vanilla Pudding Mix, eggs, milk, vegetable oil, and sour cream. Beat the mixture on low speed for approximately 30 seconds. Then, increase to medium speed for about 1 and a half to 2 minutes. Don't forget to scrape the sides of the bowl occasionally to ensure everything is well mixed.
Pour the cake batter into the prepared baking pan, smoothing it out evenly.
Bake the cake for 20 to 25 minutes. You’ll know it’s done when a toothpick inserted in the center comes out clean. Once baked, remove it from the oven and allow it to cool completely.
While the cake cools, prepare the raspberry filling. In a small saucepan, combine the frozen raspberries, sugar, and half a cup of water. Bring the mixture to a gentle boil, stirring frequently to help break down the raspberries.
In a separate small dish, mix the remaining half cup of water with the cornstarch. Slowly pour this mixture into the simmering raspberry mix. Continue to cook for a few more minutes until the mixture thickens slightly, then transfer it into a bowl and allow it to cool completely. Once it has cooled, place it in the fridge until it’s chilled.
Now, let’s prepare the cream cheese topping! In a large bowl, add the cream cheese and beat it with a mixer until it’s light and fluffy. Then, add the whipped topping and mix until fully incorporated.
Once the cake has cooled and the raspberry filling has chilled, spread the raspberry mixture evenly over the top of the cake.
Next, dollop the cream cheese mixture over the raspberry filling and carefully spread it into an even layer. This will provide a luscious topping that complements the cake perfectly.
Finally, garnish your Vanilla Raspberry Sheet Cake with fresh raspberries as desired. Keep the cake chilled until you’re ready to serve it.
