Step 1

Preheat the oven to 325 F, and position a rack in the center of the oven. Lightly spray a 9-inch tart pan with a removable bottom with nonstick baking spray.

Step 2

In a bowl, combine the melted butter with the granulated sugar and brown sugar. Use a wooden spoon to mix vigorously for 2 minutes.

Step 3

Stir in the vanilla, egg and egg yolk until smooth.

Step 4

In a separate bowl, sift together the flour, corn starch, salt and baking soda. Stir the dry ingredients into the wet ingredients, stirring just until no more flour remains. Let the dough sit at room temperature to cool for 10 minutes.

Step 5

Stir the chocolate chips into the cooled dough. The dough will be thicker now than it was before cooling.

Step 6

Scoop the dough into your prepared pan, and press the dough evenly against the bottom of the pan. Sprinkle the dough with the mini chocolate chips and the sprinkles.

Step 7

Bake for 20-22 minutes, until the cookie is puffed and the top is a light golden brown.

Step 8

Set the pan on a cooling rack and cool the cookie for 2 hours, then remove the sides of the pan, and transfer the cookie to a serving plate.

Step 9

With an electric mixer, beat all the frosting ingredients for 4-5 minutes until light and fluffy. Add a few drops of pink or red gel food coloring, if desired.

Step 10

Fit a piping bag with Tip #6B, and fill with the buttercream. Pipe a border around the edge of the cookie, and decorate with more sprinkles and mini chocolate chips.