Heat the oven to 190C/fan170C/gas 5. Line two baking sheets with non-stick baking paper. Put the butter and sugars into a bowl and beat until creamy. Beat in the vanilla and egg. Sieve the flour, bicarbonate of soda and salt into the bowl and mix it in with a wooden spoon. Add the chocolate chips and stir well. Use a teaspoon to make small scoops of the mixture, spacing them well apart on the baking trays. This mixture should make about 30 cookies. Bake for 8–10 mins until they are light brown on the edges and still slightly soft in the centre if you press them. Leave on the tray for a couple of minutes to set and then lift onto a cooling rack.