To make the pastry: combine the flour, sugar, and salt in a large mixing bowl. Add the butter and mix with a pastry blender or hands until the mixture resembles coarse crumbs. Make a well in the middle of the pastry. Combine the egg yolk with the ice water in a small bowl, whisking to blend; pour it into the well and work it in to bind the dough until it holds together without being too wet or sticky. Squeeze a small amount together, if it is crumbly, add more ice water, 1 tablespoon at a time. Form the dough into a disk and wrap in plastic; refrigerate for at least 30 minutes.
Roll out the pastry on a lightly floured surface into a 12-inch circle, about 1/4-inch thick. Carefully roll the dough up onto the pin (this may take a little practice) and lay it inside a 9-inch tart 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, especially the scalloped edges. 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 sturdy cookie sheet so it will be easy to move in and out of the oven. Line the tart with aluminum foil and add pie weights or dried beans 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 color, but not brown. Remember the tart will be cooked again with the filling. It should be cooked but light in color so that it will not burn on the second bake. Set aside to cool and lower the oven temperature to 325 degrees F.
To make the filling: Heat the heavy cream and milk in a pot over medium-low flame, until it simmers slightly around the edges. Remove from the heat; add the chopped chocolate and stir until 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 chocolate 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 set and the surface is glossy. If you see any bubbles or cracks forming on the surface, take the tart out right away - that means it is beginning to become over baked. Cool before cutting.