Preheat oven to 350 degrees.In large mixing bowl, cream butter and granulated sugar with a mixer for 1 minute until combined.Add in the eggs, sour cream, and vanilla extract. Blend until combined.Add in baking powder, baking soda, salt, and half of the flour and blend until combined.Add the other half and blend together until fully combined.Take 2 tablespoons of dough (I used a 2 Tbsp cookie scoop) and roll into a ball. Place on lined cookie sheet. Repeat with remaining dough. Using the bottom of a cup (spray with cooking spray so it won't stick) gently, very gently, press down a little bit on the dough ball so the top is flat.Bake at 350 degrees for 10-11 minutes. Remember they will cook slightly more while cooling.Let cool on cookie sheet for 5 minutes before removing to cool completely on a wire rack.To make frosting: blend butter until smooth.Add in powdered sugar and vanilla extract and blend. Add milk or cream, 1 tablespoon at a time, until desired thickness is reached.Frost cooled cookies and top with sprinkles. Makes 3 dozen cookies.