In a small mixing bowl, combine all the mug cake ingredients. Whisk until the batter is smooth. Put in the microwave for about 1 minute.Let the cake cool.
Make the cream cheese frosting
Combine all the ingredients in a mixing bowl and whisk until the frosting is light and fluffy. Top the cake with the frosting and enjoy.
Notes
Do not exceed the required amount of flour and baking soda. If you add too much flour and baking soda to the mug cake mixture, the outcome will not be smooth and rich as you expected it to become.
For perfect result, use natural cocoa powder and don't use the dutch processed cocoa powder as it may affect the cake's outcome color badly.
Use whole milk for a creamier and thicker texture, and use plant-based milk such as oat milk and soymilk if you are following a strict diet.
Too much white vinegar will ruin the desired mild chocolatey taste of this recipe, making it too acidic in taste.
Butter indeed helps in making a creamy cream cheese frosting. However, if you add too much of this to the frosting mixture, the frosting will become runny.
I recommend using gel red food color as it gives a better result than the liquid food color.