200 grams unsalted butter, cold and cut into small chunks
1 large egg, separated
2 tablespoons ice water, plus more if needed
250 milliliters double cream
120 milliliters milk
250 grams dark or plain chocolate, chopped
1/4 teaspoon salt
2 large eggs, beaten, at room temperature
1 zest of orange
To make the pastry: combine the flour, sugar, and salt in food processor. Add the butter and mix with a pastry blender until the mixture resembles coarse crumbs. Combine the egg yolk with the ice water to blend into a dough that holds together without being too wet or sticky.
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 and lay it inside a 9-inch tart pan with a removable bottom.
Press the dough into the pan so it fits tightly with an extra bit of dough that hangs outside the tart tray; 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 or piece of dough. Put the tart in the refrigerator for 15 minutes to relax.
Preheat the oven to 180.
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 baking parchment and baking beans or pie weights.
Bake for 30 minutes, then remove the paper and weights. Set aside to cool and lower the oven temperature to 160.
To make the filling: Heat the 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. Let cool to room temperature.
Add salt, zest of an orange and a beaten eggs and whisk until well incorporated.
Pour the filling into the cooled tart shell and bake for 15 to 20 minutes until the filling is set and the surface is glossy.