Did something very similar to this a few months ago. Worked lovely in the correct cup and with some fiddling depending on microwave power. Here's mine.
Easy-peasy cake. It's possible to go from ingredients to eating in 4 minutes.
What you need
1 Large mug - preferably straight sided - The large Starbucks mugs are great for this - unfortunately that means you actually have to go into Starbucks to get one - sorry about that.
4 Tablespoons plain flour
4 Tablespoons caster sugar
2 Tablespoons unsweetened cocoa
1 Egg
3 Tablespoons milk
3 Tablespoonsvegetableoil
3 Tablespoons dark chocolate chips.
1 teaspoon vanilla extract
Method:
Add the flour, sugar and cocoa into the mug and mix well.
Add the milk and oil and the egg and again, mix well.
Add the vanilla extract and the choccy chips and... you guessed it... mix well.
Stick the mug into the microwave and stick on full power for 3 minutes.
What will happen is after a couple of minutes the cake will rise up out of the mug. Once it nearly gets up to the top of the microwave, it's done - this can be anything from 2:15 to 3:00. When you switch the microwave off it will sink back into the mug - it's meant to do that.
Tip out of the mug and eat.
There are a few things you can do to change it - but experiment. The most common one that I know of is replacing the sugar and the cocoa with 4 tablespoons of instant hot chocolate mix and 2 tablespoons of caster sugar. Just experiment though - it's that quick and easy.