How to Make It
Melt the chocolate in a small saucepan set in a larger pan of simmering water; stir until smooth. Meanwhile, in a medium saucepan, combine the water with the sugar and corn syrup and bring to a boil over high heat. Whisk in the cocoa powder, reduce the heat to moderate and cook, stirring, until slightly thickened, about 3 minutes. Remove the pan from the heat and whisk in the melted chocolate and espresso dissolved in water.
In a medium saucepan, combine the sugar and corn syrup and cook over moderately high heat, without stirring, until a deep-amber caramel forms, about 6 minutes. Using a wet pastry brush, wash down any crystals from the side of the pan. Remove the pan from the heat and carefully stir in the cream and butter; the sauce will bubble up. Cook the caramel sauce over moderate heat for 5 minutes, stirring occasionally.
Spoon the ice cream into sundae glasses or bowls. Top with the hot fudge and caramel sauces, sprinkle with nuts and serve.