Cream together the butter and sugars, then beat in the egg. Sift together the flour, bicarbonate of soda and salt, and mix in. Stir in the chocolates and nuts. Form the dough into a cylinder shape, wrap in cling film and store in the fridge until needed (it will keep for up to one week).
To make the cookies, simply cut off slices and place on a greaseproof-lined tray, leaving ample space between each one. Bake for 6-8 minutes, until tan-coloured and puffy. Take out the tray and bang it on a worktop to knock out the air. Return to the oven for around 6-8 minutes, until the cookies are golden brown.
Take the tray out of the oven and again bang it on a worktop. Leave the cookies to cool on the tray, then store in airtight jars for up to a week.