Unroll the puff pastry and lay it on a sheet of baking parchment.
Score the pastry with a knife about 2 cm in from the edge, all the way round. Not deep, - just a light score mark.
Pre-bake the puff pastry in a preheated oven for 10 min at 200°C, conventional oven (top and bottom heat).Let it cool slightly before adding the topping.
Mix the sugar and cinnamon and set aside.
Spread the pastry with crème fraîche, - give it a quick stir with a spoon first if needed, so it is easier to spread.You can also warm the back of the spoon in some boiling water, – that makes it easier to spread the crème fraîche.
Crumble or grate half of the marzipan over the base, and sprinkle with 2 tablespoons of the cinnamon sugar.
Arrange the apples in a tightly packed layer on top, grate or crumble the remaining marzipan over the apples, and sprinkle with another 1 tablespoon of cinnamon sugar.
Scatter the flaked hazelnuts over the top, and spray lightly with a little cooking spray if you like. I use Lurpak spray.You can also use roughly chopped hazelnuts.
Bake the apple tart for a further 12-14 minutes, until the edge is a rich golden colour and the apples are slightly tender.Let the tart cool slightly before serving with cold crème fraîche and extra cinnamon sugar.Just before serving, you can give the top a little extra spray butter if you would like it to have a slight shine.