For chocolate bottom, melt butter and chocolate together over in a bowl placed over a pot of gently simmering water, stirring regularly. Stir in coffee and corn syrup. Add sugar, cocoa powder and salt and blend. Add cream and vanilla and continue stirring until sugar is dissolved. Pour chocolate sauce into bottom of 8 x 11-inch baking dish.
For crème brûlée, heat cream with the scraped seeds and pod of vanilla bean to just below a simmer. In a bowl, whisk together egg yolks, sugar and rum. Place bowl over a pot of simmering water and whisk vigorously until eggs are doubled in volume and hold a ribbon when the whisk is lifted. Remove from heat. Slowly pour cream into egg mixture, whisking constantly until all cream has been added. Return cream to pot, and with a wooden spoon, stir over medium-low heat until thickened and coats the back of a spoon, about 5 minutes. Remove from heat and strain. Pour brûlée filling over chocolate sauce in baking pan. Bake in a bain-marie for 50 to 60 minutes. Cool to room temperature, then chill for at least 3 hours before serving.
To serve, slice bananas lengthwise and place on top of custard mixture. Sprinkle with rum. Sprinkle with sugar and torch with a blowtorch or broil for one minute, with the oven door cracked open. Serve immediately.
Yield: 1 8 x 11-inch baking dish. Makes 8 to 10 servings.