01 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl. Set aside for later use.
02 - Beat softened butter and granulated sugar together in a large mixing bowl until light and fluffy, approximately 2-3 minutes.
03 - Add egg and vanilla extract to the butter mixture. Beat until fully incorporated, then mix in the sour cream until smooth.
04 - Gradually add dry ingredients to the wet mixture, mixing until a soft, uniform dough forms. Avoid overmixing.
05 - Divide dough in half, flatten into discs, wrap in plastic wrap, and refrigerate for at least 1 hour until firm.
06 - Preheat oven to 350°F. Line two baking sheets with parchment paper and set aside.
07 - On a lightly floured surface, roll dough to 1/4-inch thickness. Cut 2.5-inch circles and place on prepared baking sheets 2 inches apart.
08 - Bake for 9-11 minutes until edges are just set and cookies remain pale. Cool completely on wire racks.
09 - Beat softened butter until creamy. Gradually add sifted powdered sugar, beating well after each addition. Add vanilla, salt, and cream. Beat on high for 2-3 minutes until fluffy.
10 - Once cookies are completely cool, spread or pipe frosting generously on top. Add food coloring if desired and decorate with sprinkles.