1. Pre-heat the oven to 180°C.
2. To make the pastry, mix together the flour, icing sugar and salt in a food processor fitted with a dough blade. Add the butter and blend until the mixture resembles breadcrumbs. Mix in a little of the beaten egg at a time, until the pastry forms a ball, you may not need all the egg. Wrap tightly in cling-film and refrigerate for one hour. The pastry can be frozen and used at a later date.
3. Remove the pastry from the cling-film and roll out onto a lightly floured surface to 1/4cm in thickness. Line a 25cm ring with the pastry, making sure to let the pastry hang over the side - the excess will fall off during cooking. Place it on a baking sheet and put it in the fridge for 30 minutes.
4. Line the pastry with greaseproof paper and fill with baking beans to keep the base's shape, and bake blind for about 20 minutes. Remove the baking beans and greaseproof paper and return to the oven for a further five to eight minutes or until the pastry is starting to turn golden brown. Don't allow it to get too much colour as it will be returning to the oven for a further 40 minutes of cooking with the custard.
5. Remove from the oven, brush with egg yolk and place in the oven for a further five minutes. Remove from the oven and leave to cool completely. Turn the oven down to 150°C.
6. For the filling, break the chocolate into pieces put into a bowl and set aside. Bring the cream and milk to the boil and pour it over the chocolate pieces. Stir well until the chocolate and cream are mixed. Allow to cool for five minutes. Beat the eggs, then add to the chocolate and mix well.
7. Fill the pastry case with the chocolate custard. Carefully place in the middle of the oven and bake for 40-50 minutes or until the custard appears set. Remove from the oven and allow to cool to room temperature. Rest in the fridge until completely set.
8. Carefully, starting from the outside edge, cover the tart with the raspberries working towards the middle. Carefully dust the tart with icing sugar before serving.