With an electric mixer fitted with the paddle attachment, add the sour cream, butter, and sugar and beat until light, fluffy, and pale in color.
Add the egg and vanilla. Continue to beat for another 2 minutes.
In a large mixing bowl, add 3 cups of cake flour with the baking soda, baking powder, and salt. Stir to combine.
Slowly add the dry ingredients to the butter mixture and mix to combine.
Chill the prepared dough for 2 hours.
Preheat the oven to 325F. Line two sheet pans with parchment.
Scoop 2tbsp portions of dough and roll into balls with your hand. Place onto the prepared sheet pan being sure to leave several inches between each cookie. Repeat.
Using a flat surface dipped in cake flour (like the bottom of a glass,) gently press each top of cookie to evenly flatten them to roughly ¼-inch.
Top each cookie with frosting and sprinkles.