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, followed by sour cream and vanilla extract. Beat until fully incorporated and smooth.
04 - Gradually add the flour mixture to the wet ingredients, mixing just until combined. Avoid overmixing to maintain tender texture.
05 - Cover bowl with plastic wrap and refrigerate dough for at least 1 hour, or overnight. Chilling prevents excessive spreading during baking.
06 - Preheat oven to 350°F. Line two baking sheets with parchment paper and set aside.
07 - Scoop heaping tablespoons of chilled dough and roll into balls. Arrange on prepared baking sheets 2 inches apart. Gently flatten each ball to 1/2 inch thickness.
08 - Bake for 9-11 minutes until cookies appear set and edges are lightly golden. Remove promptly to prevent overbaking.
09 - Let cookies rest on baking sheets for 5 minutes, then transfer to wire rack to cool completely before frosting.
10 - Beat cream cheese and butter until creamy and smooth. Gradually incorporate powdered sugar, then mix in vanilla. Add milk 1 tablespoon at a time until desired spreading consistency is achieved.
11 - Generously spread frosting over completely cooled cookies. Top with sprinkles or colored sugar if desired. Store in airtight container in refrigerator for up to 5 days.