Combine flour, baking powder, baking soda & salt in a small bowl & SIFT WELL. Set aside.
In a large mixing bowl, combine butter & sugar. Beat on high until light & fluffy.
Add in sour cream, eggs & vanilla & beat until combined.
Lower the mixer to the lowest speed & slowly beat in the flour mixture until just combined.
Cover with plastic wrap & refrigerate for a minimum of 3 hours, but it is best to chill overnight.
Once the dough is chilled, preheat the oven to 350 degrees.
Line baking sheets with parchment & set aside.
Measure 3 tbsp of dough per cookie & use your hands to roll the dough into smooth balls of dough.
Place on the prepared cookie sheet leaving 1″ spacing between cookies.
Use the bottom of a glass to SLIGHTLY flatten each ball of dough.
Bake 11-12 minutes – the cookies will look under-baked.
Carefully transfer the cookies to a wire rack to cool.
Once the cookies have cooled to room temperature, they are ready for decorating.