Preheat the oven to 350 degrees. Grease a 9×13 inch baking pan.

Add the cake mix, water, oil, and eggs to a large bowl, and beat on high speed for 3 minutes. Pour batter into the cake pan, and bake for 28-30 minutes, or until a toothpick inserted into the center of the cake comes out clean.

Remove the cake from the oven, and let it cool completely.

To make the raspberry glaze, mix the cornstarch and sugar together in a small bowl with a whisk.

Add the raspberries and lemon juice to a small saucepan, and add the cornstarch and sugar mixture, then stir well.

Cook over medium heat for 15 minutes, stirring often, while chopping the berries with the spatula.

Once the mixture is done, refrigerate for 2 hours.

Once the cake and glaze has cooled, spread the mixture over the entire surface of the cake, then top with whipped topping.