Put the butter and sugars into a large mixing bowl. Beat together with an electric hand whisk until smooth and light in colour.
Break in the eggs one at a time, mixing as you break in each egg. Once the eggs are combined, add the vanilla extract.
Sift in the flour and baking powder and mix in with a wooden spoon until completely incorporated. Add the chocolate chunks and mix in until thoroughly combined. Divide the dough in half.
Place each half onto a large sheet of cling film. Roll the dough into a wide sausage shape and wrap in the cling film, twisting the ends to seal. Each sausage will make nine large cookies (but you can roll them smaller and make more). The dough sausages can be frozen at this point. However if you wish to bake them straightaway, chill the dough in the fridge for 30 minutes before use.
Once ready to use the cookie dough, remove from the freezer and allow to warm up enough to slice. Preheat the oven to 180C/350F/Gas 4.
Slice the dough sausage into nine discs and place onto a non-stick baking tray or a tray that has been lined with baking parchment.
Sprinkle each cookie with a tiny pinch of salt and bake in the preheated oven for 20 minutes, or until they are golden-brown on the edge and slightly paler in the centre.
Remove from the oven and transfer to a wire rack to cool before serving.