In a medium bowl, whisk flour, baking soda, and baking powder until combined. Set aside.
Place softened, salted butter and granulated sugar in bowl of a stand mixer and beat on medium-high for 3 minutes, until light and fluffy. Add eggs, one at a time, until incorporated. Add vanilla and sour cream and mix on low until combined.
Add all of dry ingredients to wet ingredients and mix on low until just combined. Do not over-mix or the dough will get tough. The dough will be sticky. Grab plastic wrap and lay out two large sheets. Separate dough onto each sheet so you have two even piles of dough. Cover dough with plastic wrap and form into a flat rectangle. Refrigerate overnight. Do not skip this step! It will be impossible to roll out the dough if it is not cold.
The next day, preheat oven to 425 degrees. Prepare two baking sheets by laying with parchment paper or using a silicone mat. Flour your work-surface and rolling pin extremely well. Don't skimp on the flour - the dough will be super sticky so we need the flour to keep it from sticking to the counter.
Remove rectangle of dough from fridge and unwrap. Flour both sides of the dough pretty well so it does not stick as we roll it out. Roll out dough until it is about 1/4 inch thick. Using a 2 1/2-inch cookie/biscuit cutter, cut out 24 rounds from the dough. You may have to combine scraps and roll out again to achieve this. Place dough on two cookie sheets (12 per sheet), about an inch apart.
Bake for 4 minutes, rotate, and bake for 4 more minutes until slightly golden on the edges. Do not over-bake! We want these to stay soft. Remove from oven and transfer cookies to wire cooling racks. Do not frost until completely cooled. Repeat process with second rectangle of dough.