In a large bowl, sift together flour, cocoa powder, baking powder, soda and salt.
In a smaller bowl, whisk together buttermilk, eggs, sugar, melted butter and vanilla extract. Add the wet ingredients to the flour mixture, stirring with a large spoon until a dough forms. Line a baking sheet with wax or parchment paper, and roll dough into balls just slightly smaller than golfball size.
Add vegetable oil to a large pot and heat over medium heat. Once it reaches 350 degrees F, add 2-3 donut holes at a time, frying for 2-3 minutes. I tossed mine a few times during the frying process, just using a slotted spoon to continually flip them over. One finished, remove with a slotted spoon and let drain on a paper towel. Once all the donut holes have been fried, dip in the glaze them set on wire rack. Allow to set for 10-15 minutes for simple glazed donuts. If you want sprinkled donuts, immediately roll in sprinkles after glazing and let sit until set.