This is a Scottish millionaire's shortbread recipe. It uses pure butter shortbread in the base and so the crust doesn't required any baking. I used white chocolate for the top layer but dark or milk could work too. In this recipe I used a tin of caramel, because I had a spare one to use up. It was a bit too squishy, so homemade caramel would probably work better, as it tends to set better: try my recipe for Caramel Sauce.