Preheat the oven to 180C/375F. In a bowl, beat the butter until pale.
Add both sugars to the bowl.
Add the egg and a few drops of vanilla essence.
Add the baking powder and salt.
Add flour in two batches. There's no need to sift the flour.
Add the chocolate chips. Using a spoon, drop the dough onto a baking sheet (do not flatten out after dropping).
Bake in the oven for 8-10 minutes at 180-185C (375F for American ovens.) If you like your cookies crispy, up to 15 minutes should be fine.
They should puff up like this after about 8 minutes. When removed from the oven, they will shrink and become nice and chewy with a soft texture.