For the donuts: ½ cup (1 stick) butter, softened 2 tsp. vanilla ⅓ cup packed brown sugar ⅓ cup granulated sugar 1 large egg ⅔ cup sour cream ⅔ cup buttermilk 1½ tsp. baking powder 1½ tsp. baking soda ½ cup cocoa powder 2 cups all-purpose flour
For the glaze: 2 cups powdered sugar 3 tbsp. milk (more if needed to thin glaze) 2 tsp. vanilla
For the topping: 7 Oreo cookies, coarsely chopped Sprinkles
Preheat oven to 425°F. Lightly grease donut pans and set aside.
In a large bowl, cream the butter, vanilla and both sugars. Add the egg, sour cream and buttermilk. Mix until well combined.
In a separate bowl, combine the baking powder, baking soda, cocoa powder and flour. Gradually add to the wet ingredients.
Fill the donut pan cavities three-quarters of the way full. Bake for 9 minutes. Allow the donuts to cool in the pan for 2-3 minutes before removing to wire racks to cool completely.
After the donuts have cooled, whisk all of the glaze ingredients in a shallow medium bowl. Dip the donuts in the glaze. Sprinkle with Oreo cookies and sprinkles.