Preheat the oven to 350F and spray a 9" baking pan or pie dish with nonstick cooking spray.
Using an electric mixer on medium speed, cream the butter until it's smooth (about 1 minute).
Add in the sugar and continue to mix for another minute, until the mixture is light and fluffy.
Add in the eggs and vanilla extract and continue to mix until well combined. Scrape down the sides of the bowl as needed.
In a medium bowl, sift together the flour, salt, baking powder, baking soda and cornstarch.
Slowly add the dry ingredients to the wet ingredients and mix until just combined.
Add in the white chocolate chips and sprinkles and either briefly use the electric mixer, or mix by hand.
Spread the cookie dough evenly in the prepared baking pan and bake for 25-30 minutes, or until very lightly browned. Allow the cake to cool in the pan for 10-15 mins and then transfer to a wire rack to cool completely. Decorate the cake with the whipped vanilla frosting once it has completely cooled.