Rhubarb and Apple Filling: Place the rhubarb, apple, caster sugar,
water and cinnamon stick in a saucepan. Place the saucepan on the stove at a
moderate heat and stir the mixture so that all the ingredients are well combined.
Leave the mixture to simmer gently for 10 minutes stirring regularly until the
rhubarb and apple is soft and tender but still holds it shape. Remove the filling
from the stove and take out the cinnamon stick. Spoon the puree into individual or a
single pie dish. Set aside while you prepare the crumble.
Oat Crumble: Place all the crumble mixture accept the oats into a
food processor and process it briefly so that you have a rough crumb mixture.
Transfer the mixture to a bowl and stir in the oats until it is well combined.
Scatter the crumble mixture all over the filling.
To Cook: Place the rhubarb crumble or crumbles into the preheated
oven and cook it for 30 minutes or 20 minutes for individual ones until the crumble
is crisp and golden brown. Remove the crumble from the oven and serve.
To Serve: Serve the individual crumbles or spoon out the crumble
into bowls, with a scoop of vanilla or lavender ice-cream or thick cream.