Sift together the flour, bicarbonate of soda and salt and set aside
Cream together the butter and sugar until light & fluffy
In another bowl, mix the egg and vanilla extract then gradually beat into the butter mixture
Stir in the peanut butter and blend thoroughly
Stir in the dry ingredients
Chill for at least 30 minutes until firm
Preheat the oven to 180°C/350°F/Gas Mark 4. Grease 2 baking sheets
Spoon out rounded teaspoonfuls of the cookie mixture and roll into balls
Place the balls on the prepared baking sheets and press flat with a fork into circles about 6cm/2½ ins in diameter, making a criss-cross pattern
Bake for 12-15 minutes until lightly browned
Transfer to a wire rack to cool
For extra crunch add 50g/2oz/½ cup chopped peanuts with the peanut butter*The next time I make these I'd use half & half light brown sugar and Muscavado sugar to give the cookies more depth of flavour.