Mug Cakes

I think mug cakes were the best inventions ever.

I know they have been around for a while now, but I only recently tried them xD They're so easy and quick to make, I don't even need lots of ingredients so it's great for my budget too :D

I only tried doing a coffee cake with very basic ingredients that I happenned to have at home (eggs, flour, sugar, milk, a bit of olive oil and instant coffee) and I was surprised it came out so well :)

What are your favorite mug cakes to do and your tips to making the best cake? :)