To make the pastry:combine the flour, sugar and salt in a large mixing bowl. Add the butter and mix in a blender or with hands until the mixture resembles coarse crumbs. Combine the egg yolk with a the cold water in a small bowl, whisking to blend. Work it in to bind the dough until it holds together without being too wet or sticky. Mix in small amount together, if it is crumbly, add more cold water 1 tablespoon at a time. Form the dough into a disk and wrap in plastic:refrigerate for 30 mins

Roll out the pastry on a lightly flavoured surface into a big circle about 1/4 inch thick. Carefully roll the dough up onto the pin and put it inside the tear pan with a removable bottom. Press the dough into the pan so it fits tightly. Press the edges into the sides of the pan. It is important to press the dough evenly into every nook and corner of the ring. Shave off the excess hanging dough with a knife. Put the tart in the refrigerator for 15 minutes to relax.

Preheat the oven to 350 degrees F.

Place the tart pan on a cookie sheet so it will be easy to move in and out of the oven. Line the tart with aluminium foil and add weights to keep the sides of the tart from buckling. Bake for 30 minutes, then remove the foil and weights. Using a pastry brush, lightly coat the crust with a beaten egg white. Return to the oven and continue to bake for another 8 minutes until the tart is golden in colour but not brown. Remember the tart will be cooked again with the filling

To make the filling: Heat the heavy cream, milk and condensed milk over medium-low flame, until it simmers slightly. Remove from the heat; add the chopped chocolate, nutella, melted and smoothed out. Add the sugar and salt and whisk until well incorporated. Beat the eggs in a small bowl until blended and add them to the mixture, stir until completely blended. Pour the filling into the cooled tart shell and bake at 325 degrees F for 15 to 20 minutes until the filling is s