Whisk flour, cocoa, baking powder and salt together in a large bowl. In a medium one, whisk eggs, sugar, sour cream or buttermilk and butter. Stir wet ingredients into dry until well blended. Chill batter until cold, at least 1 hour and up to 3.

Flour your counter generously and scrape dough onto it. Flour dough. Flour your hands. Gently pat dough out until it is 1/2-inch thick. Dip a 1 1/4 to 1 1/2-inch round cutter into a dish of flour and cut rounds from dough. Pat scraps of dough together and cut them again. If your dough or doughnut holes have gotten too soft to easily pick up, put them on a floured or parchment or waxed paper-lined tray and put them in the freezer for a few minutes, until they’re firm enough to handle again.

Prepare your fryer or fill a 5 to 6-quart with 4 inches of oil. Heat to 375°F (190°C). Fry 6 to 12 doughnut holes at a time, about one full minute on each side. Make sure you bring the oil back to 375°F after each batch.

Drain doughnut holes on a stack of paper towels. Once cool, roll in glaze and let drain and dry on cooling racks.