A triple layer of crumbly crust, a truffle-like interior, and an almost patent-leather-shiny glaze make this tart the chicest take on chocolate we've come across in a long time.
Preheat oven to 350°F with rack in middle.
Stir together chocolate graham crackers. 5 tablespoons unsalted butter, 1/4 cup sugar and press evenly onto bottom and 3/4 inch up side of tart pan. Bake until firm, about 10 minutes. Cool on a rack 15 to 20 minutes
Bring 1 1/4 cups cream to a boil, then pour over 9 ounces chocolate in a bowl and let stand 5 minutes. Gently stir until smooth. Whisk together eggs, vanilla, and salt in another bowl, then stir into melted chocolate.
Pour filling into cooled crust. Bake until filling is set about 3 inches from edge but center is still wobbly, 20 to 25 minutes. (Center will continue to set as tart cools.) Cool completely in pan on rack, about 1 hour.
Bring 2 tablespoon cream to a boil and remove from heat. Stir in 1 3/4 ounces chocolate until smooth. Stir in corn syrup, then warm water
Pour glaze onto tart, then tilt and rotate tart so glaze coats top evenly. Let stand until glaze is set, about 1 hour.
Tart is best the day it is made but can be made, without glaze, 1 day ahead and chilled. Bring to room temperature before glazing.