Preheat the oven to 350°F (175°C).
Make the crust: combine the finely ground chocolate graham crackers (about 1 cup crumbs), melted butter (5 tablespoons), and 1/4 cup sugar in a bowl until evenly moistened.
Press the crumb mixture evenly into the bottom and up the sides of a greased 9-inch tart pan to form the crust.
Bake the crust for 10 minutes, then transfer to a cooling rack and cool about 20 minutes.
For the filling: bring the cream to a boil in a saucepan, then pour it over chopped chocolate in a heatproof bowl; let sit 5 minutes.
Gently stir the chocolate and cream until smooth. In a separate bowl, whisk together the eggs, vanilla, and salt, then fold the egg mixture into the melted chocolate until combined.
Pour the filling into the cooled crust and bake until the filling is set about 3 inches from the edge but the center still jiggles, about 25 minutes.
Let the tart cool; it will finish setting as it cools.
Make the glaze: bring cream to a boil, remove from heat, and stir in chopped chocolate until smooth. Stir in corn syrup, then stir in the warm water.
Pour the warm glaze onto the cooled tart and tilt or rotate the tart so the glaze spreads to cover the filling; let stand until the glaze is set.
Remove the tart from the pan, place on a serving platter, and cut into wedges to serve.