Additional whipped cream and chocolate curls, optional
In a heavy saucepan, bring water to a boil; stir in coffee until dissolved. Reduce heat; add marshmallows and butter. Cook and stir over low heat until marshmallows are melted and mixture is smooth.
Set saucepan in ice and whisk mixture constantly until cooled. Fold in whipped cream; spoon into pastry shell. Sprinkle with nuts. Refrigerate for at least 3 hours before serving. Garnish with whipped cream and chocolate curls if desired.