Preheat oven to 180 degrees C. Grease baking trays.
In a large bowl, cream together the butter, brown sugar, white sugar, salt and peanut butter. Beat in the eggs and vanilla. Combine the flour and bicarb soda; stir into the batter to form a dough. Mix in the chocolate chips and walnuts. Scoop mounds of dough as large as two tablespoons onto the prepared baking trays. Biscuits should be at least 5cm apart. Flatten biscuits down by 1/3 using the bottom of a glass.
Bake for 10 to 12 minutes in the preheated oven, until well risen and brown. Do not overbake they will firm up a little as they cool. Allow biscuits to cool on baking tray for 5 minutes before removing to a wire rack to cool completely.