01 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl until well combined. Set aside for later use.
02 - Beat softened butter and granulated sugar in a large mixing bowl on medium-high speed for 2-3 minutes until light and fluffy, scraping down sides as needed.
03 - Add egg and vanilla extract to the butter mixture. Beat until fully incorporated, then mix in sour cream until smooth.
04 - Gradually add dry ingredients to wet mixture on low speed, mixing just until a soft dough forms and no flour streaks remain.
05 - Divide dough in half, shape into flat discs, wrap tightly 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 chilled dough to 1/4-inch thickness. Cut into 2.5-inch rounds and place 2 inches apart on prepared baking sheets.
08 - Bake for 9-11 minutes until edges are set but centers remain soft and pale. Cool on baking sheets for 5 minutes before transferring to wire rack.
09 - Beat softened butter until creamy. Gradually add sifted powdered sugar, beating well after each addition. Mix in vanilla, salt, and cream. Beat on high for 2-3 minutes until fluffy. Add food coloring if desired.
10 - Once cookies are completely cool, spread or pipe frosting generously on top. Add sprinkles immediately if using before frosting sets.