01 - Whisk together flour, baking soda, baking powder, and salt in a medium bowl. Set aside for later use.
02 - Beat softened butter and granulated sugar in a large bowl until light and fluffy, approximately 2-3 minutes.
03 - Mix in the egg until incorporated, then blend in sour cream and vanilla extract until fully combined.
04 - Gradually add dry ingredients to the wet mixture, mixing just until flour disappears. Avoid overmixing to maintain tenderness.
05 - Cover dough with plastic wrap and refrigerate for minimum 1 hour or overnight. Chilling prevents spreading and enhances texture.
06 - Preheat oven to 350°F. Line two baking sheets with parchment paper for easy cleanup.
07 - Scoop heaping tablespoons of dough, roll into balls, and place 2 inches apart on prepared sheets. Flatten gently to 1/2 inch thickness.
08 - Bake for 9-11 minutes until set with lightly golden edges. Remove promptly to prevent drying.
09 - Let cookies rest on baking sheet for 5 minutes, then transfer to wire rack to cool completely before frosting.
10 - Beat cream cheese and butter until creamy. Gradually incorporate powdered sugar until smooth. Mix in vanilla and adjust consistency with milk.
11 - Generously frost cooled cookies. Add sprinkles immediately if desired. Store in airtight container refrigerated for up to 5 days.