Pre-heat oven to 180°C (160°C fan-forced). Line oven trays with baking paper.
Place butter and sugar in the large bowl of an electric mixer. Beat until pale and creamy. Add egg, mixing well. Fold in the peanut butter.
With mixer on low speed, gradually add flours, mixing until a dough has formed. Remove bowl from stand and fold in the chocolate and peanuts with a spoon. Form dough into tablespoon measures of balls and flatten slightly when placing on trays. Bake for 20 minutes. Allow to cool on a cooling rack.