Ingredients 
150g dark chocolate, broken into pieces
1 tsp vanilla bean paste or extract
125g butter, room temperature
175g light brown soft sugar
1 egg, beaten
175g plain flour
25g cocoa powder
1 tsp baking powder
100g milk chocolate, chopped into chunks
100g white chocolate, chopped into chunks

Method
Preheat the oven to 180c and line 2 trays with silpat liner or baking paper/parchment.

Put the dark chocolate in a microwaveable bowl and put on full power for 30 seconds then stir and continue zapping for 30 seconds and stirring until the chocolate is mostly melted. Add the vanilla and stir again. Put to one side to cool a little.

Using a stand mixer or hand held whisk, mix the butter and sugar until the butter is pale and the mixture smooth and creamy. Whisk in the egg until fully incorporated and then mix through the melted dark chocolate.

Put a sieve over the bowl and pour in the flour, cocoa powder and baking powder and sift in, breaking up any lumps. Mix through until just combined. Stir through the chocolate chunks.

Take an ice cream scoop (or tbsp) of the dough and put on to the trays, far apart and bake for 12-15 minutes.  Check them after 10 minutes, it is difficult to tell when chocolate cookies are done but they will start to set around the edges and go darker, you don’t want them to go too dark and bitter.  I tend to do 6 at a time and while one batch is cooling I bake another and find they mostly take 12 minutes.  If you want giant cookies then take 2 or 3 scoops mould them together and put on the tray and bake.