- Preheat the oven to 160 degrees. Add the chopped rhubarb, sugar, finely chopped ginger and a little water to a pan and saute until they begin to break down and form a compote.
- Meanwhile, grate the apple roughly and add to the compote. Bring to the boil and let it cool down immediately.
- For the crumble, mix granola, sugar and rapeseed oil.
- Cut the sponge cake into strips and place in an ovenproof dish. Pour the apple juice over the top and leave to soak briefly before you add the fruit compote.
- Spread the crumble on top and bake in the oven for about 20 minutes.