1. Make the Dough: In a large mixer bowl, whisk together flour, sugar, yeast, baking powder, salt, and cocoa powder. In a separate jug, combine warm buttermilk, eggs, melted butter, vanilla, and red food coloring. With the mixer running on low using a dough hook, slowly pour the wet ingredients into the dry ingredients. Mix for 2–3 minutes until a very sticky dough forms. Cover the bowl and let rise in a warm place until doubled in size, about 60–90 minutes.

2. Cut the Donuts: Turn the risen dough onto a heavily floured surface. Gently pat to about ½-inch thickness. Use a floured 3-inch cutter to cut rounds. Use a 1-inch cutter for donut holes. Re-roll scraps once if needed.

3. Fry the Donuts: Heat oil in a heavy Dutch oven over medium heat until it reaches 350°F. Carefully slide 2–3 donuts into the oil using a slotted spoon, avoiding overcrowding. Fry for 60–90 seconds per side until deep reddish-brown and lightly hollow-sounding when tapped. Transfer to a wire rack to drain.

4. Make the Glaze: Beat softened cream cheese until completely smooth. Gradually beat in powdered sugar and vanilla. Add milk one tablespoon at a time until thick but pourable.

5. Glaze the Donuts: Dip one side of each slightly warm donut into the glaze. Place back on the rack to allow excess glaze to drip off. Let set before serving.

6. Optional Filling: If using custard filling, allow donuts to cool completely. Fit a piping bag with a Bismarck tip, fill with custard, insert into the side of each donut, and gently pipe until slightly filled.