1. Preheat the oven to 190C/170C fan/gas 5. Line two baking trays with non-stick baking paper.
2. Put the butter and sugars into a bowl and beat until creamy. Beat in the vanilla extract and egg. Sieve the flour, bicarbonate of soda and salt over the mixture and mix in with a wooden spoon. Add the chocolate chips and stir well.
3. Using a teaspoon, place small mounds of the mixture well apart on the baking trays. Bake in the oven for 8–10 mins until light brown on the edges and still slightly soft in the centre.
4. Leave on the tray for a couple of minutes to firm up and then transfer to a cooling rack.