01 - In a medium bowl, whisk together flour, baking powder, baking soda, and salt until well combined. Set aside for later use.
02 - In a large mixing bowl, beat the softened butter and granulated sugar together on medium speed until light and fluffy, approximately 2-3 minutes.
03 - Add the egg and vanilla extract to the butter mixture. Beat until thoroughly incorporated, scraping down the sides as needed.
04 - Mix in the sour cream until fully combined with the wet mixture.
05 - Gradually add the dry ingredients to the wet mixture, mixing on low speed until a soft, cohesive dough forms. Avoid overmixing.
06 - Divide the dough in half and flatten into discs. Wrap tightly in plastic wrap and refrigerate for at least 1 hour to firm up.
07 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
08 - On a lightly floured surface, roll out the dough to 1/4-inch thickness. Cut into circles using a 2.5-inch round cutter and place on prepared baking sheets, spacing 2 inches apart.
09 - Bake for 9-11 minutes until edges are just set and centers remain slightly soft. Cookies should appear pale, not browned. Cool completely on wire racks.
10 - Beat softened butter until creamy. Gradually add sifted powdered sugar, beating well after each addition. Add vanilla, salt, and cream. Beat on high speed for 2-3 minutes until light and fluffy. Add food coloring if desired.
11 - Once cookies are completely cool, spread or pipe frosting generously on top of each cookie. Add sprinkles immediately if desired, before frosting sets.