Cut the rhubarb into 7½cm/3in long sticks and place on an oven tray and sprinkle with 4 tablespoons of water and the caster sugar. Roast for 10 minutes. Sprinkle over the ginger and mix well.
Fill an ovenproof dish about 4cm/1½in deep with the rhubarb.
Rub the butter into the flour and sugar to make the crumble topping. Sprinkle over the rhubarb and bake for 35–45 minutes
or until the crumble topping is crisp and golden-brown and the rhubarb filling has softened and is bubbling.
Allow to cool slightly before serving with double cream.
