Preheat oven to 350°F (175°C). Line baking sheets with parchment.
Mix dry ingredients; set aside. Beat butter and sugar until fluffy. Add egg and vanilla; combine. Mix in dry ingredients. Fold in sprinkles.
Portion dough with a cookie scoop, shape into balls, flatten slightly. Bake 9-11 minutes until edges are set but not browned.
Cool cookies, then shape into circles if desired. Prepare frosting by beating cream cheese and butter, then add vanilla, salt, powdered sugar, and heavy cream until stiff peaks form.
Pipe frosting over cooled cookies, sprinkle with Christmas sprinkles before serving.
Notes
Ensure frosting is not overwhipped to prevent splitting. Use cold heavy cream for best frosting texture.