For the cookie base:
1 cup butter, softened
8 oz cream cheese, softened
1½ cups sugar
2 teaspoons vanilla extract
2½ cups flour
1 teaspoon baking powder
½ tsp baking soda
For the frosting:
3/4 cup salted butter, room temperature
3 cups powdered sugar
1 teaspoon vanilla extract
3-4 tablespoons heavy cream
Preheat oven to 350ºF. Prepare a 9×13 jelly roll pan or baking dish by lining it with parchment paper or foil and lightly spraying with cooking spray.
Use an electric mixer to beat together the butter and cream cheese until smooth. Mix in the sugar, and be sure to scrape down the sides of the bowl.
Mix in the egg and the vanilla.
Add the flour, baking powder, and baking soda. Mix until soft dough forms.
Spread the dough evenly in the pan or dish. Bake for 20 minutes. Let cool completely before frosting (recipe follows) and cutting.
For the Frosting:
Use an electric mixer to whisk the butter until it’s smooth.
Add the powdered sugar one cup at a time with 1 tablespoon at a time of the vanilla or the heavy cream until all the ingredients have been added and the frosting is smooth. Be sure to scrape down the sides of the bowl as you go.
Frost the cooled cookies and add the sprinkles.
Source : allrecipes.Com