01 - Whisk together flour, baking soda, baking powder, and salt in a medium bowl until thoroughly combined. Set aside for later use.
02 - Beat softened butter and granulated sugar in a large bowl until light and fluffy, approximately 2 to 3 minutes.
03 - Mix in the egg until fully incorporated, then add sour cream and vanilla extract. Beat until smooth and uniform.
04 - Gradually add dry ingredients to the wet mixture, mixing just until flour disappears. Avoid overmixing to maintain tender texture.
05 - Cover dough tightly with plastic wrap and refrigerate for at least 1 hour or overnight. Chilling prevents spreading and ensures thick, soft cookies.
06 - Preheat oven to 350°F. Line two baking sheets with parchment paper for easy cleanup and to prevent sticking.
07 - Scoop heaping tablespoons of chilled dough and roll into balls. Place on prepared baking sheets 2 inches apart. Gently flatten each ball to 1/2 inch thickness.
08 - Bake for 9 to 11 minutes until cookies appear set and edges are barely golden. Avoid overbaking for optimal softness.
09 - Let cookies rest on baking sheets for 5 minutes, then transfer to a wire rack to cool completely before frosting.
10 - Beat cream cheese and softened butter until creamy and smooth. Gradually add powdered sugar, mixing until fully incorporated. Stir in vanilla extract. Add milk 1 tablespoon at a time until spreadable consistency is reached.
11 - Generously spread frosting over completely cooled cookies. Top with sprinkles or colored sugar immediately if desired.