In a small bowl, mix together the flour, sugar, and salt.

Using a pastry cutter, large-tined fork, or a food processor on pulse setting, cut the chilled butter into the flour until it resembles coarse sand with a few pea-sized pieces of butter still visible.

Sprinkle the cold water onto the mixture and toss gently a few times, just until it forms a ball that holds together.

Separate the dough into two balls, flatten slightly into thick disk shapes, wrap in plastic wrap, and chill for several hours before working with it.

Preheat an oven to 375 F. Roll and trim the dough to make a circle large enough to fit a 10-inch fluted tart pan. Fit the circle into the bottom and up the sides of the pan.

Line the dough with pie weights or dried beans and bake it for 15 minutes. Remove the pie weights and bake the shell for an additional 5 minutes. Set aside the pastry shell, still in the tart pan, to cool.

In a small saucepan set over low-medium heat, bring the cream to just simmering.

Remove it from the heat, and stir in the chocolate and vanilla until the mixture is smooth and the chocolate is completely incorporated.

Whisk a small amount of the hot chocolate cream into the eggs. Transfer the tempered egg mixture back into the hot chocolate and whisk the mixture until it is smooth.

Pour the chocolate filling into the prepared pastry and bake it for 18 to 25 minutes, until most the filling is set and only the center jiggles slightly when the tart is moved.