Step 1

Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper, leaving an overhang on the sides.

Step 2

Make the cookie dough: In a medium bowl, whisk the flour, cornstarch, baking powder, and salt. Set aside.

Step 3

In a large bowl, beat the butter and sugar with an electric mixer on medium speed until light and fluffy, about 2-3 minutes. Turn the mixer to low and blend in the egg, yolks, sour cream, vanilla, and almond extract, if using. Add them one by one, mixing well between each addition.

Step 4

Add the dry ingredients and mix by hand with a spatula until just combined. Press the soft dough evenly into the prepared pan.

Step 5

Bake for 15-20 minutes until lightly golden at the edges and just barely brown in the middle. Set aside to cool fully in the pan.

Step 6

Make the frosting: In a large mixing bowl, beat the butter until creamy. Slow blend in the powdered sugar, vanilla, and salt. Add the milk, as needed, until it reaches the desired consistently. It should be light, fluffy, and spreadable (not pourable).

Step 7

Lift the cookie bars out of the pan and spread the frosting evenly over the top. Add the sprinkles, if desired then leave to set for a 10-15 minutes. . When the frosting is no longer sticky to the touch, cut the bars into squares and enjoy!