01 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl until thoroughly combined.
02 - Beat softened butter and granulated sugar in a large mixing bowl until light and fluffy, approximately 2-3 minutes.
03 - Incorporate egg and vanilla extract into the butter mixture, beating until fully blended. Mix in sour cream until smooth.
04 - Gradually add dry ingredients to wet mixture, mixing until a soft dough forms. Avoid overmixing.
05 - Divide dough in half, flatten into discs, wrap in plastic, and refrigerate for at least 1 hour.
06 - Preheat oven to 350°F and line two baking sheets with parchment paper.
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 set but not browned. Cool completely on wire rack.
09 - Beat butter until creamy. Gradually add powdered sugar, then vanilla, salt, and cream. Beat on high 2-3 minutes until fluffy.
10 - Frost cooled cookies generously. Add food coloring to frosting or sprinkles as desired.