Preheat oven to 180℃/350℉. Prepare some baking trays with sheets of baking paper.
Cream butter, sugars and vanilla. (I do this by hand with a wooden spoon but you do.)
Add egg gradually, beating well after adding.
Sift in flour and salt.
Add chocolate chips and walnuts and mix. Decide at this point if you want to add more chocolate chips.
Take heaped teaspoons of the mix and shape into balls. Put them on the baking paper, allowing room for them to spread
Bake 10-12 minutes.