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 - Add egg to the butter mixture and beat well. Mix in sour cream and vanilla extract until fully incorporated.
04 - Gradually add dry ingredients to the wet mixture, mixing just until combined. Avoid overmixing to prevent tough cookies.
05 - Cover dough with plastic wrap and refrigerate for at least 1 hour or up to overnight. Chilling is essential for proper texture and handling.
06 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
07 - Scoop heaping tablespoons of 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 9-11 minutes until cookies appear set and edges are barely golden. Avoid overbaking for optimal softness.
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 add powdered sugar, beating until smooth. Mix in vanilla extract. Add milk 1 tablespoon at a time until spreadable consistency is reached.
11 - Generously frost each completely cooled cookie. Add sprinkles or colored sugar immediately if desired.
12 - Store cookies in an airtight container in the refrigerator for up to 5 days. Unfrosted cookies can be frozen for up to 2 months.