Ingredients
250g butter 
2 tbsp cocoa powder 
140g dark chocolate, broken into cubes 
60g milk chocolate, broken into cubes 
200g flour 
200g caster sugar 
4 eggs 
4 egg yolks

Method
Firstly put both the dark and light chocolates along with 200g of the butter into a microwaveable bowl and heat gently in the microwave stirring at 30 second intervals.  When you are sure that all of the chocolate has melted, remove it from the microwave and leave to cool.  This will take between 1 - 2 minutes. 

I like to use 180ml pudding basins which I butter and then coat with cocoa powder. With the remaining butter, butter 8 pudding tins and then put 2 tbsps of cocoa powder in one tin, you then want to tip into the next tin while twisting it so you coat every part - this is what stops it sticking.

Mix the eggs, egg yolks and sugar together until thick and the pale like a really thick milkshake, expect this to take up to 10 minutes.  Add the flour and gently fold through with a large metal spoon going around the edge and cutting through the middle.  You want to mix through the flour but you don’t want to lose any of the air you just spent 10 minutes working on.

Gently fold through half of the chocolate in the exact same way.  When the chocolate is fully incorporated put the other half and repeat. 

You can now keep in the fridge until you want them.  When you want to eat them preheat the oven to 180c and cook for 12-14 minutes until when you touch the top they feel spongey. Remove from the oven and leave for a minute or two before gently running a knife around the edge and easing out.  

- Original recipe taken from here