Peel, quarter and core the apples, then slice them as finely as possible. Arrange the apple slices on top of the tart so they overlap and fan out from the centre of the tart, completely covering the pastry. Cover the apples with baking paper and put another baking tray on top to keep the apple slices flat while cooking. Bake for 15 minutes, then remove the top tray and baking paper and cook for another 30 minutes, or until the pastry is crisp underneath. Take out and brush with just enough butterscotch to cover the surface in a thin layer. Put back in the oven for 5 minutes. Leave to cool for 10 minutes before serving with the rest of the sauce.