Chocolate Mascarpone Cheesecake with Fruit and Nuts served with Creme Fraiche

First of all, place all of the hazelnuts for the base and the filling into the oven and toast to a golden brown; use a timer and have a look after 5 minutes, giving them 5 extra if they need it.

Then remove them from the hot tray to cool. Set aside 4 oz (110 g) for the filling. Meanwhile, make the base of the cheesecake by crushing the biscuits in a polythene bag with a rolling pin – not too finely, though, as it's nice to have a fairly uneven texture then chop the remaining 2 oz (50 g) toasted hazelnuts. Tip all the crushed biscuit crumbs into a bowl, then add the chopped nuts and melted butter and mix everything very thoroughly before packing into the base of the cake tin, pressing it very firmly all over.

Now place the tin in the oven and pre-bake the crust for 20 minutes. Then remove it and let it cool while you make the filling. Reduce the oven temperature to gas mark 2, 300°F (150°C).

To make the filling, first place 2 inches (5 cm) of water into a saucepan, then put the saucepan on to heat and, meanwhile, break the chocolate into small squares and place this into a basin. As soon as the water is boiling, remove the pan from the heat and place the bowl on top until everything melts. Don't be tempted to put the bowl on top of the saucepan while the water is still boiling – because of the high cocoa solid content, this chocolate mustn't get overheated or it will separate.

Now spoon the mascarpone and fromage frais into a large bowl and whisk them together until smooth, preferably with an electric hand whisk. Then add the eggs and sugar and give it another good whisking before adding the melted chocolate – use a rubber spatula so that you get every last bit of chocolate from the basin – and then lightly fold the chocolate into the egg mixture. Finally, add the raisins and toasted hazelnuts. Now pour the mixture into the tin, smoothing it out with the back of a spoon, then place it on the centre shelf of the oven and bake for 1¼ hours.

After that, turn the oven off but leave the cheesecake inside until it's completely cold. To make the chocolate curls: melt the chocolate as before, then pour it on to a flat, smooth surface. The underside of a large plate will do. It should form a circle of about 6 inches diameter (15 cm) and ¼ inch (5 mm) thick. Place the plate into the fridge to chill for 45 minutes.

What you want is the chocolate to be set hard enough so that if you press the surface of the chocolate it doesn't leave an indentation. Now take it from the fridge and use a cheese slicer, otherwise a sharp knife will do if you hold the blade in both hands. Just pull it all along the chocolate towards you and it should curl up. What is very important to know here is that if it doesn't curl and you end up with a pile of chocolate shavings they'll look just as nice – either way, place them in a rigid plastic container and then put this in the fridge until you need them.

To serve the cheesecake, sprinkle the surface with chocolate curls, dust with a sprinkling of cocoa powder and serve in slices with crème fraîche or cream, handed round separately.