Preheat the oven/air fryer to 180°C
Slice the rhubarb into small dice size pieces.
Place into a baking dish and sprinkle with 100g brown sugar.
Place the flour and sugar in a bowl and rub the butter in until it looks like fine breadcrumbs.
Stir in nuts.
Scatter the crumble over the rhubarb.
Bake for 25 - 30 minutes in the oven until the topping should be golden brown
Serve with whipped cream or vanilla ice cream.
