01 - In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
02 - In a large mixing bowl, beat the softened butter and granulated sugar together until light and fluffy, about 2-3 minutes.
03 - Add egg and vanilla extract to the butter mixture; beat until well combined. Mix in the sour cream.
04 - Gradually add the dry ingredients to the wet mixture, mixing until a soft dough forms.
05 - Divide the dough in half, flatten into discs, wrap in plastic wrap, and chill 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 out the dough to 1/4-inch thickness. Cut out circles about 2.5-inch diameter and place them on the prepared baking sheets, spacing them 2 inches apart.
08 - Bake for 9-11 minutes, until the edges are just set. Do not let them brown. Let cookies cool completely on a wire rack.
09 - In a large bowl, beat the 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. Mix in food coloring if desired.
10 - Once cookies are completely cool, spread or pipe frosting generously on top. Decorate with sprinkles if desired.