Preheat the oven to 180/160Fan/350F. Grease and line a couple of baking trays.
Cream the butter and sugars together until very light and fluffy.
Slowly add the beaten eggs until the mixture is smooth. Add the vanilla.
Sift together the flour, baking powder and bicarbonate of soda. Stir into the batter just until everything is incorporated. Fold in the chopped chocolate or chips.
Using an ice cream scoop, drop spoonfuls of the cookie batter onto the lined trays. You can roll the mixture into balls using your hands (this cookie dough is a dream to work with) but I find I get the best results using an ice cream scoop. This way you’ll have perfect, evenly sized cookies.
Bake for 5 mins, then remove the tray from the oven and sharply (and carefully!) bang the tray down on a solid work surface a few times to deflate the cookies.
This will expel the air in the cookies and give you gorgeous, squidgy chewy cookies!
Return the cookies to to the oven and bake for a further 7-10 minutes or until golden around the edges.
The cookies will still be quite soft in the middle, so leave them on the baking tray for 5 minutes before transferring to a wire rack.