In medium saucepan over medium heat, add 10 oz whipping cream and hazelnut spread. Cook 5 minutes, stirring occasionally. Do not boil. Once smooth, set aside to cool.
Using stand mixer, add condensed milk, remaining whipping cream, and hazelnut mixture. Whip 20 minutes until soft peaks form. Fold in marshmallows.
Pour mixture into 13x9-inch baking dish. Drizzle top with hazelnut spread.
Freeze 6 hours or overnight.
Note: Extended freeze time required.