To grind graham cracker pieces; place in food processor and grind in short pulses to a fine crumb consistency. Do not over-pulse as it may clump together. (Or place crackers in sealed bag and crush with heavy object by hand)
In medium bowl, mix graham cracker crumbs, melted butter, and salt till well blended. Press mixture into bottom and sides of 8 or 9 inch pie pan.
Bake at 350º for 7-10 minutes, or until firm. Allow to cool slightly.
Place chocolate chips and butter in small bowl. Microwave in 30 second increments, stirring in-between, until melted. Pour into crust and spread evenly on bottom with spatula. Place in refrigerator for at least 10 minutes to harden chocolate.
In a medium bowl, beat cream cheese and heavy cream until thick. Beat in Nutella until just combined. Spoon mixture into crust and evenly spread with spatula.
Cover and refrigerate for at least 2 ½ hours.
Before serving. Top with marshmallow and slightly press into filling to stick. Broil pie in oven with lid open, about 8 inches from heat, for 2-3 minutes or until marshmallow are golden brown. (Watch carefully to prevent burning)