Add the eggs and beat it well. Also add the milk, melted butter (or oil) and vanilla extract, mix well together and stir well to combine with the cake mix so all the ingredients are combined evenly. Now the batter for the mug cakes is ready!
Add about ¾ cup of batter to a large size microwave safe mug. It's a good idea to keep a microwave safe plate under the mug so in case the batter boils over (that's why we need a big sized mug!) that will be caught in the plate!
Microwave for about 1 minute and 30 seconds until the cake is done! It might look too soft when you take it out of the microwave but give it a couple of minutes and it will e just perfect! The cake might turn hard in texture if you heat for more time, so if you feel the need to cook it further, heat for another 15 to 20 seconds and then see if it's done to your liking!
Serve the cake warm with a cup of tea or coffee for best results!
Similarly, you can make mug cakes using the remaining batter. If you want to save the batter for later use, you may refrigerate for another couple of days but for the best results, it's best to make all mug cakes and you can refrigerate the prepared cakes and enjoy the cakes throughout the week as you like!