For the cookies: Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper.
In a stand mixer fitted with the paddle attachment, cream together the granulated sugar and butter until fluffy and pale. Add the eggs and mix until incorporated, then add in the vanilla and finally add the sour cream, mixing until well blended.
Sift together the flour, baking powder, baking soda and salt. With the mixer set to low speed, add the dry ingredients to the butter and mix until well combined. Chill in the refrigerator for about 20 minutes.
Dust a clean surface with flour. Roll out the dough and cut into shapes with cookie cutters. Place each on the prepared baking sheet and bake for 12 minutes. Cool the cookies completely.
For the frosting: In a stand mixer fitted with the whip attachment, whip the butter until soft and creamy. Add the confectioners' sugar, milk, vanilla and salt. Cream together until fluffy. Spread the frosting over the cookies, about 2 heaping tablespoons per 3-inch cookie.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.