Chocolate Walnut Pie with Chocolate Fudge Sauce

Ingredients:
9 oz plain flour
1 oz icing sugar, plus extra to dust
6 oz cold butter
3 large eggs
5 oz dark chocolate, roughly chopped
5 ozwalnuts, lightly toasted
6 oz caster sugar
1 egg yolk
Chocolate fudge sauce and cream, to serve
Chocolate fudge sauce
3 1/2 cups sugar
6 oz Dutch cocoa powder
2.5 oz unsalted butter
Method
Preheat oven to 350 F. Sift the flour and icing sugar into a medium bowl, add the butter and a pinch of salt. Use your fingers to rub together until it resembles fine breadcrumbs (or use a food processor). Add 1 whole egg and mix together until you have a smooth dough. Wrap in plastic wrap and refrigerate for 30 minutes.
Whizz the chocolate and walnuts in a food processor until they are a medium fineness, place in a bowl and add the caster sugar and remaining whole eggs. Stir to combine.
Bring the pastry to room temperature and reserve one third for the lid. Roll out the remaining pastry on a lightly floured surface to 1/5 inch thick and use to line a 4 x 14 inches lightly greased loose-bottomed tart pan (check for leaks).
Roll out the reserved pastry to 1/5 inch thick. Pour the filling onto the pastry base, moisten the edges with a little water and carefully place the pastry on top. Gently press edges together to seal, and trim any excess pastry. Make 3 small slits in the lid to allow steam to escape.
Beat the egg yolk with a little water and brush over top of tart. Bake for 35 minutes until golden.Set aside in the pan to cool then transfer to a serving plate and dust with icing sugar. Serve sliced with chocolate fudge sauce and cream.
Chocolate fudge sauce: Place sugar in a pan with 3 1/2 cups of water. Cook over low heat, stirring until sugar dissolves. Simmer for 15 minutes then whisk in sifted cocoa powder. Simmer for 10 minutes, add butter and stir until dissolved. Set aside to cool.