1. Grease a round tin with butter/margarine and preheat the oven to 180°C.
2. In a saucepan, melt the Zùsto with the water over a medium heat until it turns golden brown (caramel). This will take about 5 to 10 mins, so in the meantime, peel the apples – see step 4.
3. Remove the pan from the heat and add the cold butter/margarine. Stir until everything is uniform.
4. Peel the apples and remove the core using an apple corer. Cut the apples into 2.
5. Pour the mixture into the baking tin (spread with a palette knife over the bottom of the tin) and arrange the apples over it, with their curved side facing downwards. Cover with the sheet of puff pastry and press the sides around the apples. In the center of the puff pastry, make a small hole with a knife so that any steam can escape during baking.
6. Bake for 25 min in the preheated oven. Leave to cool for 30 minutes. Take a large round plate and place it on top of the cake. Now, with a certain amount of flair (!) turn the cake tin (with the plate on top) upside down so that the cake ends up on the plate.
7. Serve the cake while still warm with a scoop of sugar-free ice cream. Read the article to discover which ice cream goes perfectly with this Tarte Tatin.

Enjoy!