Preheat the oven to 220C/450F/Gas 7. Line a baking tray with baking parchment.
Rub the flour and butter together in a bowl using your fingertips until the mixture resembles breadcrumbs. Stir in the caster sugar until well combined.
Mix in the cream tablespoon by tablespoon until the contents of the bowl come together as a soft dough. You may not need all the cream.
In a separate bowl, mix together the grated apple, cinnamon and one teaspoon of demerara sugar until well combined.
Lightly dust a work surface with a little flour. Roll the dough out into a rectangular shape the thickness of 0.5cm/¼in.
Remove the apple mixture from the bowl using a slotted spoon, so that as much juice as possible is left in the bowl. Spread the apple mixture all over the pastry.
With the long side of the pastry rectangle facing you, roll up the pastry like a Swiss roll. Using a sharp knife, cut the pastry roll into seven thick slices.
Place each pastry swirl flat onto the lined baking tray, arranging them in a circle with one in the centre. Sprinkle over the remaining demerara sugar. Bake in the oven for 20-25 minutes, or until crunchy on top and golden-brown. Serve immediately.