Preheat your oven to 180°C and line a large baking tray or two with baking paper.
In a large bowl, cream the butter and sugar together. You can use an electric whisk to make this step easier.
Add the vanilla extract and the egg and whisk again.
Add all of the flour. Mix it into the wet mixture and when it starts to stick together, use your hands to press it into a ball of dough.
Add the chopped chocolate and gently knead it into the dough.
Divide the dough into 10 equal-sized pieces and roll into balls.
Place the cookies on the baking tray, making sure to leave plenty of space in between to allow for spreading- these cookies are HUGE! I usually make 4 or 5 per tray.
Bake the cookies for 10-12 minutes until slightly firm around the edges. They will look pale and undercooked when they come out of the oven but resist the urge to keep baking them or they'll end up crunchy!
Leave the cookies on the baking tray until completely cool before enjoying.