Preheat your oven to 180C/160C Fan/375F and line two-four baking trays with parchment paper. Mine are quite large trays (40cm) to make sure the cookies don't touch!
Mix together the butter and both sugars until light and fluffy and thoroughly combined! Using an electric mixer is far easier for this because it gets very fluffy and perfect!
Mix in the vanilla and the egg until thoroughly combined, then mix in the cocoa powder, flour, bicarbonate of soda, baking powder and salt until a thick paste/cookie dough is formed.
Fold in the chocolate chips, and spoon the mixture onto the trays and make sure they are suitable spread out so they stay separate! (I usually fit 6-8 on each tray to be safe) I also use a 5cm cookie dropper/ice cream scoop to make them identical sizes.
Bake in the oven for 10-12 minutes until spread out perfectly crinkly. A minute or so less will be gooey, a minute or two more will be beautiful and crunchy.
Once baked, remove from the oven and gobble them all up - don't burn yourself on the chocolate!
TOP TIP - If they look a little too domed for you still when they're fresh out the oven, tap the tray's onto the work surface a couple of times and the cookies will flatten out a smidge - leave to cool fully on the tray still.
They are super super gooey when warm so you could serve them with a dollop of ice cream if you like (vanilla is perfect with it) and they are an utter crowd pleaser.
If you wanted to just use one type of chocolate you could as well, I just always stick to the same amount weight wise!