Preheat the oven to 350°F (177°C). Lightly grease two 6-cavity donut pans and set aside.
In a medium bowl, sift together the flour, sugar, baking powder, salt, and cocoa and set aside.
In a large mixing bowl, whisk together the egg, buttermilk, butter, oil, and vanilla until combined. Add the vinegar and red food coloring (if used) and whisk to combine. Then add the dry ingredients and stir just until combined.
Transfer the batter to a piping bag and cut off the tip. Pipe the batter into the prepared donut pans until the cavities are about ¾ full.
Bake for 10-11 minutes or until a toothpick inserted into the center comes out clean. Let cool for about 10 minutes, then remove from the pan and transfer to a wire rack to cool completely.
Place the chopped chocolate, butter, light corn syrup, and water in a heatproof bowl and melt in the microwave. Stir every 20 seconds. Then, let cool for a few minutes.
Dip the tops of the cake donuts into the glaze and decorate as desired. Store in an airtight container in the refrigerator for up to 3 days.