Preheat the oven to 180°C (Gas Mark 5). Mix the sugar, flour, oats and salt (if desired). Rub in the butter until the mixture forms clumps.
Spread out on a tray and bake until turns golden (10-20mins). Cool.
Sprinkle the crumble on top of the ice cream just before serving.
Triple Motion: Apple Crumble Ice cream https://www.triplemotion.com/2012/12/09/apple-crumble-ice-cream-and-peanut-butter-and-jelly-ice-cream/