For the Donuts

1. Preheat your oven to 350 degrees Fahrenheit. Spray donut pan with cooking spray. If using a silicone donut mold, place molds on top of a baking sheet for easier removal from the oven.
2. In a medium bowl, whisk all purpose flour, cocoa powder, baking powder, baking soda, and salt together.
3. In a large bowl, whisk vegetable oil, granulated sugar, light brown sugar, vanilla extract, room temperature egg, room temperature sour cream, and buttermilk together.
4. Add dry ingredients to wet ingredients, whisking slowly and carefully. Whisk until the dry ingredients are just combined, meaning just until you see all of the dry ingredients disperse into the mixture. Overmixing will lead to dry and dense donuts.
5. Transfer batter to a Ziploc bag or piping bag if desired, cutting off the corner or tip respectively. Fill donut molds about 2/3 full to avoid the donuts from overflowing while baking.
6. Bake donuts for 12-16 minutes or until a toothpick inserted into the center comes out with moist crumbs. The tops should not look wet and should spring back when poked. Continue baking until donuts reach this point.
7. Allow donuts to cool for at least 20 minutes before removing from the mold to finish cooling on a wire rack.

For the Glaze

1. In a medium bowl, mix powdered sugar, and 2 tablespoons of milk together. Glaze should be thick. You should be able to easily lift your spoon from the bowl and have the glaze slowly but consistently fall off of the spoon. Glaze should not look wet or runny at all.
2. If glaze is too thick to stir and does not easily fall off of a lifted spoon, add an extra teaspoon of milk until desired consistency is reached. If mixture is too thin, add powdered sugar by the tablespoon until desired consistency is reached.

To Decorate

1. Use a spoon or knife, spread about 1-2 tablespoons of glaze on top of each donut. Begin by adding glaze towards to the middle of the donut, as some will likely fall over the edges.
2. Add pieces of crushed Oreos to freshly glazed donuts. Oreo pieces will not stick to the donut if they have set, so make sure to add them shortly after adding the glaze!
3. Allow the donuts to set before enjoying! Store donuts, covered, at room temperature for up to 4 days!