Pre-heat your oven to 160C Fan/180C/350F/Gas 4, and line a couple of baking trays (or however many you own) with baking paper
Melt the dark chocolate in a glass bowl over a pan of shallow water on a very low heat. Make sure the water does not touch the bowl. Or you can melt it in the microwave, start with a 30 second blast then continue with 10 second blasts, stirring in between, until it's fully melted
In a bowl mix together the light brown sugar and butter
Add the egg and vanilla extract and mix well
Add the self raising flour and cocoa powder and mix in
Then pour in the melted dark chocolate and mix well
Add the chocolate chips. then cover the bowl and chill the mixture for 15 minutes in the fridge
Scoop the mixture out with a spoon or your hands and roll each piece into a ball and flatten it down a little with your hands. Place onto the lined baking trays. Leave space in between them as they will expand when baking
Bake for 8-12 minutes. The timing will depend on your oven, so aim for 10 minutes, then adjust as needed. They will come out of the oven very soft and will seem unbaked, but then will harden up as they cool
Leave them on the tray for at least 5 minutes to harden, then move to a cooling rack
Store in an airtight container and eat within 3 days, they can also be frozen