1. Preheat the oven to 170°C. Place the flour and the cold butter in a large bowl and rub them together with your fingertips. Add half of the sugar and rub again, until all the ingredients come together and have a crumb-like texture. You want a mixture of large and small clumps/ clusters.
2. Cut the rhubarb into 2-3 cm chunks. Place in a large bowl and sprinkle with the remaining sugar. Add Lyle’s Golden Syrup, stir together, and set aside for 20 minutes, stirring every now and then.
3. Transfer the rhubarb with all the juices into an ovenproof dish, and sprinkle the crumble topping over it. Place in the oven and bake for 45-50 minutes, until golden brown and bubbly around the edges. Remove from the oven, and serve while warm, with ice cream, custard, or cream.