Preheat the oven to 350 degrees.
In a bowl, whisk together the 2 ¼ cup all purpose flour and 2 tsp salt.
2 ¼ cup all purpose flour, 2 tsp salt
In the bowl of an electric mixer, cream together the 1 cup unsalted butter and 1 cup granulated sugar at medium speed for about 2 minutes. Add the 1 egg + 1 egg yolk and 2 tsp vanilla extract and beat until fluffy, for about 5 minutes.
1 cup unsalted butter, 1 cup granulated sugar, 2 tsp vanilla extract, 1 egg + 1 egg yolk
Add the dry ingredients to the butter mixture and mix until a dough forms.
Lay the dough onto a lightly floured surface and pat into a circular round. Cut the round in half so that you have two even pieces.
Line to loaf pans with parchment paper.
Press one piece of the dough into an even layer on the bottom of a loaf pan. Repeat with the other pan and piece of dough.
Bake for 30 minutes until the center is no longer doughy.
Remove from the oven and let cool until the cookies reach room temperature. Once room temperature, remove the two baked pieces from the pan and wrap in parchment paper. Chill in the refrigerator for 30 minutes.
Meanwhile, cream together the 1 cup unsalted butter and ½ cup cream cheese in the bowl of an electric mixer until smooth. Add the 4 cups powdered sugar one cup at a time, incorporating completely between each addition. Add the 2 tsp vanilla extract and 2 tbsp heavy cream and beat on medium-high speed for about 3 minutes until the frosting is light and fluffy.
1 cup unsalted butter, ½ cup cream cheese, 4 cups powdered sugar, 2 tsp vanilla extract, 2 tbsp heavy cream
Spread an even layer of frosting onto the two rectangular pieces of cookie. Slice the pieces vertically into 6 pieces each for a total of 12 pieces.
Sprinkle with the rainbow sprinkles before serving.
rainbow sprinkles