In a large bowl, mix together the all-purpose flour, cocoa powder, sugar, baking soda, baking powder, and salt.
In a separate bowl, mix together egg, melted butter, buttermilk, vanilla, and white vinegar.
Add wet ingredients to dry ingredients and whisk until combined.
Oil or spray donut pan, and spoon or pipe donut batter until it's ¾ filled.
Bake donuts at 350℉ for 10-15 minutes or until inserted toothpick comes out clean. Let cool completely.
For cream cheese glaze, mix together softened cream cheese, powdered sugar, and vanilla in electric mixer.
While the electric mixer is on low, slowly add milk until the glaze is thin consistency to coat the donuts.
Line a baking tray with parchment paper and dip donuts one by one in glaze.
Lay all the glazed donuts on the tray and refrigerate until glaze sets.