2/3cup(2.3 ounces or 65 grams) cocoa powder, preferably Dutch-process
1 3/4cups(7.88 ounces or 223 grams) all-purpose flour
1cuppacked light brown sugar
1stick (4 ounces) butter, melted
For the icing:
2cups(8.8 ounces or 250 grams) powdered sugar, sifted
8Oreo cookies, crushed
Make the doughnuts:
Preheat the oven to 350°F. Lightly greasy two standard 6-cavity doughnut pans. In a large bowl, whisk together the cocoa powder, flour, sugar, baking powder, baking soda, and salt. In a medium bowl whisk together the eggs, milk, vanilla, and vinegar. Add to the dry ingredients with the melted butter and stir until combined. Scoop the batter into a zip-top plastic bag or piping bag, cut a hole in one corner, and pipe the batter into the doughnut molds, filling about 3/4 full. Bake for 12 to 15 minutes, or until a toothpick inserted into the center comes out clean. Let cool in pans for 2 minutes before flipping the pans upside down over a rack to remove the doughnuts.
Make the icing:
Whisk together the sugar, milk, and vanilla until smooth and combined. The mixture will be very thick. Dip the tops of the doughnuts in the icing or use a spoon to spread a thick layer. Sprinkle with crushed Oreo cookies before letting set for about 20 minutes, or until the icing is slightly hardened. Serve or store in an airtight container at room temperature for up to 2 days. You may microwave the doughnuts for 15 seconds before serving to refresh.