- 3/4 cup chocolate wafer crumbs (from about 15 cookies such as Nabisco Famous Chocolate Wafers)
- 1 teaspoon instant-espresso powder
- 2 tablespoons unsalted butter, melted
- 1 pt premium coffee ice cream, softened slightly
- 1 pt premium coconut sorbet, softened slightly
- 3 tablespoons heavy cream
- 1 tablespoon light corn syrup
- 1 tablespoon packed dark brown sugar
- 1 teaspoon unsweetened Dutch-process cocoa powder
- 1/8 teaspoon salt
- 2 oz fine-quality bittersweet chocolate (not unsweetened), finely chopped
- 1 tablespoon unsalted butter
- 1 teaspoon vanilla
- Special equipment: a 1 1/2-qt rectangular mold such as a 12- by 3 1/4- by 2 3/4-inch pté mold; parchment paper; an offset metal spatula
- Put oven rack in middle position and preheat oven to 375°F.
- Line mold with a double layer of parchment paper, allowinga few inches of overhang along each side.
- Stir together crumbs, espresso powder, and butter and press over bottom of mold. Bake until crisp, about 10 minutes, then cool completely in mold on a rack, about 20 minutes.
- Scoop and drop ice cream and sorbet alternately into mold in 1 layer until crust is covered, then smooth with offset spatula until flat. Make another layer in same manner. Freeze, covered with plastic wrap, until firm, at least 2 hours.
- Bring cream, corn syrup, brown sugar, cocoa, salt, and half of chocolate to a boil in a 1- to 1 1/2-quart heavy saucepan over moderate heat, stirring until chocolate is melted. Reduce heat and simmer, stirring occasionally, 5 minutes, then remove from heat.
- Add butter, vanilla, and remaining chocolate and stir until smooth.
- Cool fudge sauce to warm, at least 15 minutes.
- Pour warm sauce over ice cream layer and freeze again, uncovered, until firm, about 15 minutes. Remove cake by grasping both ends of parchment, and transfer it to a platter. Using a spatula to stabilize end of cake, carefully slide parchment out from under cake.