Place unopened jar of Nutella in a pan of hot water and let sit 10 minutes (or heat 1 cup in a bowl in a microwave set on high for 10 to 15 seconds). Spoon chocolate ice cream into cookie crust and use a spatula to smooth surface. Drop teaspoonfuls of Nutella (about 1/2 cup) on top of ice cream. Place in freezer for 15 minutes. Spoon caramel ice cream over Nutella and return to freezer for 15 minutes. Drizzle remaining 1/2 cup of Nutella over top of caramel ice cream. Top with hazelnuts, if desired. Freeze until firm, 3 hours or overnight.
Before serving, allow pie to sit at room temperature 10 minutes. Cut slices with a large knife dipped in warm water and dried with paper towels. Drizzle a small amount of caramel syrup on dessert plates and top with a slice of pie.