For the caramel cake soufflé, first preheat the oven to 180 °C.
Bring the syrup, sugar and butter to the boil and simmer at a lower temperature until the sugar has dissolved. Mix whipped cream and mascarpone and stir into the sugar-butter mixture.
Cut the cake into slices and place in an ovenproof dish, overlapping a little. Pour the caramel sauce over it and bake the caramel cake soufflé for about 15-20 minutes.