Method

• 1.
  For the pastry, place hazelnuts in a food processor and pulse until finely chopped. Add 40g flour and grind once more into a fine mixture, but take care not to grind it for too long or it will start to go oily. Add remaining flour, then add the icing sugar, chilled butter and a good pinch of salt. Process briefly until the mixture looks like fine breadcrumbs. Add the egg yolk and about 1 1/2 tablespoons iced water, then pulse until the mixture comes together in a ball (adding a little more water if necessary, 1 teaspoon at a time). Turn out onto a lightly floured surface and knead briefly until smooth. Enclose in plastic wrap and chill for 20 minutes.

• 2.
  Thinly roll out the pastry on a lightly floured surface and use to line a 28cm loose-bottomed tart pan that’s 4cm deep. The pastry is quite short so if it breaks, just overlap the pastry edges and press back together. Prick base here and there with a fork, then chill for 30 minutes.
• 3.
  Put a baking sheet into the oven and preheat it to 190°C. Line the pastry case with a crumpled sheet of baking paper, cover the base with a thin layer of pastry weights or uncooked rice and bake on the baking sheet for 15-20 minutes until the edges are biscuit coloured. Remove the paper and weights and bake for a further 5 minutes. Remove once more, brush the base with a little of the eggwhite, then return to the oven for 3-4 minutes until the base is crisp and golden. Set aside. Lower the oven temperature to 170°C.
• 4.
  Place the milk, cream and sugar in a saucepan over medium heat and slowly bring to the boil, stirring. Take off the heat, then stir in the chocolate until smooth. Lightly beat the eggs together, then whisk into the chocolate mixture until smooth. Pour the mixture into a jug.
• 5.
  Peel and slice bananas, then arrange in an even layer over the base of the pastry case. Return tart base to the oven, then pour in the filling. Carefully slide the oven shelf back in, then close the door. Bake the tart for 25-30 minutes until the filling is just set but still has a slight wobble. (It will continue to firm up as it cools.) Leave to cool, then cut into wedges and serve.