In a small or medium bowl, whisk the flour, cocoa powder, baking powder, baking soda, and salt together. Set aside.
In a separate large bowl, whisk the sugar, oil, buttermilk, vinegar, vanilla, and red food coloring until combined.
Pour the dry ingredients into the wet ingredients, and mix until the batter is smooth and thick. Carefully spoon the batter into a microwave-safe, 12-ounce mug. It will fill about ⅓ of the cup.
Microwave the cake at high power for 1-2 minutes (depending on the microwave wattage) or until the cake has risen to the top of the mug and a toothpick inserted into the middle comes out clean.
Let the cake rest for five minutes, then top with cream cheese frosting, if desired, and enjoy warm.