Preheat the oven to 180℃ (160℃ fan)/350°F/gas mark 4. Lightly grease a 25cm (10in) loose bottom cake tin
Beat the butter and sugar together until light and fluffy. Add the egg and vanilla and beat well.
Sift the flour and bicarbonate of soda into the bowl and beat to combine. Stir in the chocolate chips. Tip the mixture into the cake tin and press out level (Emilie does this with lightly wetted fingers).
Bake the cookie 30 minutes, until risen and golden and a skewer inserted into the centre of the cookie comes out clean.
Allow to cool in the tin. Serve cut into wedges
Nutrition information is calculated using an online nutrition database - is approximate and is meant as a guideline only.