• In a large bowl, cream butter and sugar until light and creamy. You can use a stand mixer fitted with a paddle attachment or a large bowl and electric hand mixer.
• Add the sour cream, eggs, and vanilla. Beat well, stopping to scrape the bottom and sides of your bowl, to incorporate ingredients until smooth.
• Add the flour, baking soda, baking powder, and salt and beat on low until dry ingredients are combined.

  The dough will be very soft and this is what we’re looking for. Refrigerate overnight.
• Preheat oven to 350°F. Portion cookies using a tablespoon or cookie scoop. Portion cookies and roll into a ball between hands. Add cookie balls to a greased baking sheet.
• Bake for 11-12 minutes until the center is set and the edges are just starting to turn a light golden brown.
• Let sit on the baking sheet for 5 minutes, then transfer to a cooling rack.

  Allow cookies to cool completely before frosting.

To make buttercream frosting:

• Cream the butter in a large bowl using a stand mixer with a paddle attachment or a hand mixer.
• Add the powdered sugar and mix on low-speed until all of the sugar is combined.

  Add in milk, 1 tablespoon at a time and vanilla extract to reach desired consistency.