Mix all the cake ingredients together in a medium bowl until smooth and there are no lumps.
Pour the mixture into a mug - you want to ensure your mug has enough room left over for the cake to rise without overflowing.
Microwave on high for 60s.
Whilst the cake cools, make the frosting by mixing the cream cheese, icing sugar and cocoa powder.
Once the cake has completely cooled, top with the frosting and enjoy.
Notes
Yogurt - This recipe uses 0% fat natural yogurt but you can use any 0% fat yogurt. You can replace with a dairy free alternative which would make this recipe completely vegan! Espresso - I used espresso powder for this recipe but you can totally use an espresso shot or granulated coffee - I've tried both and they work great. If using an espresso shot - leave out the boiling water. If using granulated coffee/instant coffee - mix the coffee with the boiling water until its completely dissolved then add to the rest of the ingredients. If you are not a fan of the taste of coffee - you can leave the espresso out. Microwave - My microwave is 700W and the cake took 60 seconds to cook. If you're using a different wattage microwave, divide 42,000 by the wattage of your microwave to get the amount of time for your mug cake to be done in your microwave.