Chocolate Truffle Tart

FOR CRUST

chocolate wafers such as Nabisco Famous, finely ground in a food processor (1 1/2 cups)

unsalted butter, melted and cooled completely

FOR FILLING

fine-quality bittersweet chocolate (no more than 60% cacao if marked), coarsely chopped

stick (6 tablespoons) unsalted butter, cut into 1/2-inch cubes

large eggs, lightly beaten

heavy cream

granulated sugar

salt

pure vanilla extract