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 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 thoroughly combined, then mix in sour cream.
04 - Gradually incorporate dry ingredients into the wet mixture, mixing until a soft, cohesive dough forms.
05 - Divide dough in half, flatten into discs, wrap in plastic wrap, and refrigerate for at least 1 hour.
06 - Preheat oven to 350°F. 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 sheets, spacing 2 inches apart.
08 - Bake for 9–11 minutes until edges are set but not browned. Cool completely on wire racks.
09 - Beat softened butter until creamy. Gradually add sifted powdered sugar, mixing well after each addition. Add vanilla, salt, and cream. Beat on high speed for 2–3 minutes until fluffy. Add food coloring if desired.
10 - Spread or pipe frosting generously onto cooled cookies. Top with sprinkles if desired.