Preheat oven to 400°. Line a baking sheet with a silpat or parchment paper. Set aside.
In a stand mixer fitted with the paddle attachment, or in a large mixing bowl using a hand mixer, cream together the butter and sugar until smooth and light in color.
Add in the sour cream, eggs, vanilla extract, and additional flavored extract, if using. Mix until just combined.
In a separate mixing bowl, sift together the flour, baking powder, baking soda, and salt. Add the dry ingredients to the wet in three additions—mixing well after each.
Roll dough into 2″ balls and place 2″ apart on the prepared cookie sheet. Use a roller (a mini roller works great) to roll cookies flat (about 1/4 to 1/2 inch thick).
Bake cookies in preheated oven 7 minutes. They will not be brown when done. Remove from oven and transfer from cookie sheet to cooling rack. Allow cookies to fully cool before frosting.