Apple is a great substitute for rhubarb, you will need 4 -6 apples depending on size. Oats, chopped hazelnuts, walnuts and almonds can be added to the crumble mix, cinnamon also make a nice addition too.
1 bunch of rhubarb
55 g (1/4 cup) caster sugar
150 g soft butter, diced
250 g (1 2/3 cups) plain flour
150 g (3/4 cup firmly packed) soft brown sugar
Trim off the leaves and root ends from the rhubarb and cut into 2 cm chunks. Heat a heavy-based pot over medium heat. Add rhubarb, sugar and 2 tbsp water
Reduce the heat to low, cover with a lid and cook for 5–10 minutes, stirring often. The rhubarb should be reduced to a chunky paste. Remove from the heat and allow to cool.
Preheat oven to 180°C (350°F).
Rub together soft butter, flour and brown sugar until they resemble fine breadcrumbs. Place stewed rhubarb into a baking dish, top with crumble mixture and bake in preheated oven for 20 minutes, or until golden brown.
Serve with cream or custard.