Make the Cookie Dough:

1. Whisk the Dry Ingredients: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
2. Cream Butter and Sugar: In a large mixing bowl, use an electric mixer to beat the butter and granulated sugar until light and fluffy, about 2-3 minutes.
3. Add Wet Ingredients: Beat in the egg and vanilla extract, followed by the sour cream, until fully incorporated.
4. Combine Wet and Dry: Gradually add the dry ingredients to the wet ingredients, mixing until just combined. The dough will be soft.
5. Chill the Dough: Cover the dough with plastic wrap and refrigerate for at least 1 hour to make it easier to handle.

Bake the Cookies:

6. Preheat the Oven: Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper.
7. Shape the Cookies: Scoop tablespoons of dough and roll them into balls. Place them on the prepared baking sheets, spacing them about 2 inches apart.
8. Flatten Slightly: Use the bottom of a glass or your palm to gently flatten each dough ball.
9. Bake: Bake for 10-12 minutes, or until the edges are set but the centers are still soft. Do not overbake.
10. Cool: Allow the cookies to cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.

Make the Frosting:

11. Cream the Butter: In a medium bowl, beat the softened butter with an electric mixer until smooth.
12. Add Sugar and Cream: Gradually add the powdered sugar, heavy cream, and vanilla extract, beating until fluffy. Add food coloring if desired.
13. Frost the Cookies: Spread the frosting over the cooled cookies using a knife or offset spatula.
14. Decorate: Add festive sprinkles on top while the frosting is still soft.