Preheat oven to 400 degrees.
In a large bowl cream together butter and granulated sugar for 2 minutes on medium speed.
Add in eggs and vanilla and mix until well blended.
In a separate bowl whisk together flour, cornstarch, baking powder, baking soda and salt then slowly add to the wet ingredients.
Blend until the flour is halfway incorporated. You don't want to over mix the dough.
Add in the sprinkles and finish mixing until the flour is just incorporated.
Using a large cookie scoop* or 1/4 cup measuring cup, scoop dough and evenly space out 6 onto a large baking sheet. I like to set them 2, then 1, 2 and 1.
Bake for 12-14 minutes or until lightly golden brown on the bottom.
Cool for 10 minutes before frosting.