I always use Kosher salt in my kitchen! If using table salt, start with half the amount and adjust to taste, as it is much "saltier" by volume.
Instructions
In a small bowl, stir together the baking soda and sour cream. Set aside until needed.
In the bowl of a mixer, fitted with a paddle cream together the butter and sugar.
Add the salt, vanilla, baking powder and egg. Mix on medium speed for 1 minute, until combined. Now mix in the sour cream and baking soda mixture. Mix well.
Add the flour and ¼ cup of the sprinkles. Mix on low speed just until the flour is fully incorporated. Cover the bowl and refrigerate overnight.
Preheat oven to 350°F. Line a baking sheet with parchment paper. Scoop two heaping tablespoons per cookie, press the tops in the remaining sprinkles and place on the baking sheet.
Bake for 12-13 minutes, or until the edges are just starting to turn light brown. Enjoy!
Notes
The dough must be chilled! I've tried baking them after just two hours of chilling and they weren't as good. The overnight chill is worth it!