1. Preheat oven to 350 degrees Fahrenheit. Remove ice cream from the freezer. Let thaw for approximately 30 minutes to soften while you make the crust.
2. To make the crust, place pretzels, brown sugar and margarine into a food processor. Pulse until completely crumbled. Press down into a nine-inch springform pan. Bake for 10 minutes. Let cool.
3. Add ice cream, chocolate hazelnut spread, sugar, vanilla and salt to a food processor fitted with the S blade. Pulse a few times until the ice cream is completely smooth. Pour into cooled pretzel crust.
4. Top with nut crunch or Viennese crunch topping. Freeze until ready to serve.