1.Melt butter; cool. Preheat the oven to moderate (180°C/160°C fan-forced).
2.Meanwhile, combine the sugars, sifted flours and peanuts in a large bowl.
3.Add combined butter, egg and peanut butter; mix to a soft dough. Stir in the chocolate bits.
4.Place two level tablespoons of biscuit dough about 6cm apart on baking paper lined oven trays. Bake in a moderate oven for about 15 minutes or until browned lightly. For chewier cookies, bake a few minutes less; for crisp cookies, bake a few minutes longer. Cool on trays.
Suitable to freeze, baked or unbaked. Butter suitable to microwave. This recipe can be made a week ahead; Store in an airtight or glass container.