Place the flour, sugar, egg and butter in a food processor and blend until the mixture comes together in a ball of dough. Cover with clingfilm and chill in the fridge for at least 30 minutes. Remove cling and roll thinly. Line 6 greased tins with the pastry and put some greaseproof paper on top and fill with dried beans Bake the pastry ‘blind’ in a hot oven at 170°C for 10-15 minutes, or until the pastry is starting to cook, but is not quite golden yet.
To make the filling, mix the egg yolks and sugar until they are light and frothy. Fold in the crushed and chopped walnuts. Then stir in the crème fraiche. Whip up egg whites until they form stiff peaks and fold into the mixture. Pour into the individual tartlets and bake in the oven at 180°C for 15-20 minutes, until the top is golden. Remove from the oven and leave to cool.
For the topping whisk the Armagnac and icing sugar together until it’s a smooth consistency and spread this evenly over the cooled tartlets. Mix the Mascarpone and cream together and serve alongside the tart. Lastly, coat half a walnut with gold leaf and place on top of the tart.
Mix the Mascarpone cheese and the cream and beat until thick, make a quenelle of the mixture and place alongside the tartlet.