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1
Preheat the oven to 350 degrees. Mix the crumb ingredients until moistened and press into the bottom and sides of a 9-inch tart pan with a removable bottom. Bake about 8 minutes, or until the crust is fragrant. Remove it from the oven and using the flat bottom of a glass, immediately press down all over the bottom of the tart to keep it flat. Let it cool completely. Once cool, place the banana slices evenly on the bottom, in a single layer.
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2
Sift the cornstarch, cocoa, and sugar into a large heavy saucepan and whisk well. Slowly stir in the milk, 1 cup cream, and salt, and then the melted chocolate. The chocolate won't completely blend in at this stage, but it will as the mixture heats. Bring to a low boil over moderate heat, stirring constantly. Let it bubble until thickened, 1 or 2 minutes, and them remove it from the heat. Whisk the egg yolks in a separate bowl, and slowly add about 1 cup of the hot milk mixture, steadily mixing, and then slowly pour back the egg/milk mixture into the saucepan with the rest of the milk, whisking constantly. Keep whisking, and cook over moderate heat until very thick, and the temperature reaches 200 degrees. Remove from the heat and whisk in the butter, vanilla and rum.
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3
This step isn't essential, but it does make for a smoother custard: Strain the filling mixture into the crust using a coarse sieve, pushing it through with a rubber spatula. You'll see that there are some little egg and cornstarch lumps that won't go through, and the custard will be much nicer for it. But if a few lumps don't bother you, just pour the custard right in. Press some plastic wrap on the top and chill for a few hours.
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4
Whip the 1 1/4 cups cream till stiff, adding the vanilla and confectioners sugar to taste. Keep in mind that the chocolate custard is sweet, so you'll want to go easy on the sugar in the topping. You can spread it on top of the chocolate, or you can pipe it on using a pastry bag fitted with a star tip. Sprinkle on your garnish of choice.
