Direction :

1. Combine butter and cream cheese in the bowl and of a stand mixer and beat until fluffy. Add sugar; beat until even fluffier. Add egg and vanilla and mix well.
2. In a separate bowl combine the flour, baking powder, and salt. Add it to the butter and cream cheese mixture and beat until just combined. Transfer a quarter of the dough to the center of a piece of plastic wrap or wax paper. Pat into a disk, and wrap tightly. Repeat with the remaining three quarters. Chill for at least an hour and up to three days.
3. Preheat your oven to 325º F. Roll out our dough on a lightly floured surface or in between two sheets of parchment paper to 1/2-inch thick. Cut out your cookies with cookie cutters of your choice. Gather scraps, re-roll, and repeat the process.
4. Bake on parchment-lined cookie sheets for 15 to 18 minutes, or until the edges just begin to turn golden—cookies will be pale with light golden edges. Remove them from the pan and transfer to a wire rack. Cool completely. Note: I don’t like baking more than one sheet of cookies at a time, but do as you like. 
5. Meanwhile, make the frosting: Stir together the confectioner’s sugar with 1 tablespoon of the milk. Add more milk a tablespoon at a time to achieve a thick but pourable consistency. Spoon icing onto cookie, spreading to cover. Shower with sprinkles.