Cube the very cold butter and rub in until a crumb is achieved.
Mix in the butterscotch and chocolate with your hands.
As you mix it should start to come together.
Turn out into a large (40cm x 29cm), well-greased, non-stick tin, spread evenly and press down firmly with the flat of your hand.
Score into 16 equal portions with a sharp knife.
Bake in a preheated oven at 180C (160C fan assisted) for 25 mins or until firmed up and just turning a pale golden on top.
Allow to cool for 5 minutes, then re-score the pieces.
When cool enough to handle but NOT completely cold, start in a corner and lift out carefully with a small spatula or fish knife.
TIP 1: If the biscuits have stuck and you can’t get them out whole, put the tray over a low burner for just a few seconds. This re-softens the butterscotch and allows you to lift the biscuits out easily.TIP 2: Using a large tray and baking for the full 25 minutes will give a thin, crisp, well browned biscuit. If you want a more traditional shortbread, just halve the tray size to around 20cm x 15cm and take out as soon as it’s firm at the edges for a chunkier, softer biscuit.