1. Preheat oven to 350°F (175°C) and line two baking sheets with parchment paper.

2. In a medium bowl, whisk together flour, baking powder, and salt. Set aside.

3. In a large bowl, beat butter and sugar until light and fluffy (2-3 minutes).

4. Add eggs one at a time, then beat in vanilla and sour cream until combined.

5. Gradually add the dry ingredients to the wet ingredients and mix just until a soft dough forms.

6. Scoop 2-tablespoon portions onto baking sheets and gently flatten the tops.

7. Bake for 10-12 minutes, until edges are set but tops remain pale and matte.

8. Let cookies cool on pan for 5 minutes, then transfer to wire rack to cool completely.

9. To make frosting: Beat butter until creamy. Slowly mix in powdered sugar, then vanilla and milk until fluffy.

10. Add food coloring if desired, frost cooled cookies, and top with sprinkles.