Preheat oven to 350°. Line a 10-inch cake pan or springform pan with parchment paper. Set aside.

Cream butter, both sugars, and vanilla until light and fluffy, about 3 minutes. Add egg and yolk, mixing well after each addition. 

Slowly add flour, cornstarch, baking powder, and salt and mix until combined. Add chocolate chips and sprinkles.

Press dough into the pan and even out as much as possible. 

Bake for 25 to 30 minutes or until edges just begin to turn golden brown.

Remove from the oven and set on a wire rack. Cool in pan until completely cool. When cool, use a sharp knife to loosen the sides of the pan. Turn out onto a plate or serving dish. 

To make the frosting, beat the butter in an electric mixer until pale in color, about 3 minutes. Add half of the powdered sugar and beat until completely incorporated. Add the remaining powdered sugar, vanilla, and salt. Add 1 tablespoon cream and beat until light and fluffy, another two minutes. If it is too stiff, add an additional tablespoon of cream.

Add to a piping bag fitted with a star tip and pipe around the edges of the cookie. Decorate with Valentine's sprinkles.