In a large bowl, cream together the butter, brown sugar and white sugar until light and fluffy. Beat in the egg, then stir in the vanilla.
Combine the flour, bicarbonate of soda and salt; gradually stir into the creamed mixture. Finally, stir in the chocolate and peanut butter chips. Drop rounded spoonfuls onto an unprepared baking tray.
Bake for 8 to 10 minutes in the preheated oven. Allow biscuits to cool on baking tray for 5 minutes before removing to a wire rack to cool completely.
Peanut Butter Chips
If you can't find the peanut butter chips (and yes they can be hard to find in Australia, unless you order online, or through a specialist US outlet) replace with 1 cup (250g) peanut butter. Try the crunchy over the smooth!