Sift the flour into a large bowl. Lightly rub in the butter with your fingertips, until the mixture resembles breadcrumbs. Stir in the sugar, then the egg yolk and water mixture, and use a round-bladed knife to bring everything together.
Use your hands to form a dough, handling it as little as possible. (Alternatively, make the dough in a food processor to save time.) Wrap the dough in clingfilm, then chill in the fridge for 20 minutes.
Preheat the oven to 200°C, fan 180°C fan, gas 6. Roll out the pastry to a thickness of 0.5cm, then cut into 6 pieces. Line 6 individual 10.5cm tart tins with the pastry and chill in the fridge again for 20 minutes.
Line the pastry cases with baking parchment and fill with baking beans or uncooked rice. Bake 'blind' for 15 minutes, then remove the paper and beans and bake for a further 2 minutes, or until golden.
Pour or brush the melted chocolate around the inside of the tart cases and allow it to harden for 5 minutes in the fridge. Divide the caramel evenly into the pastry cases and top with the banana slices. Whisk the double cream until it forms stiff peaks, then spoon on top of the tarts. Dust with the cinnamon and cocoa powder and serve.
Cook’s tip: this is delicious served with half-fat crème fraîche.