toppings: caramel sauce, powdered sugar, pecans (such as Diamond of California pecan halves)
In one mug, whisk the egg, oil, food coloring, buttermilk, and vanilla. Add the sugar, cocoa powder, flour, baking powder, salt, and vinegar and whisk until smooth.
Transfer half of the batter to the second mug. Microwave one mug at a time for 60-90 seconds until fluffy but firm. Repeat with second mug. Top with caramel sauce, powdered sugar, and pecans as desired. Enjoy!