Preheat oven to 170 degrees celsius.
Line two baking trays with parchment paper.
Using an electric mixer or wooden spoon cream the butter and sugars together until light and fluffy.
Gradually add the beaten egg
Gradually add the flour and mix on slow speed
Add the pistachios and chocolate chunks and mix in gently.
Add the vanilla extract and then the bicarbonate of soda and mix well.
Roll small handfuls of the cookie dough into balls
Place on a baking tray and press down lightly with palm of your hand.
Make sure to leave plenty of space as the cookies will spread.
Bake at 170 degrees celsius for 15-18 minutes
This mixture makes 12/13 large cookies