Preheat oven to 180°C/350°F.
Mix all the crumble ingredients well and set aside approximately 170g (1 ½ cups) of the mixture for topping.
Press down the remaining crumble mix into a baking dish and bake for 10 minutes at 180°C/350°F.
After baking, top with jam or preserve of your choice while the crumb base is still hot so that it can spread easily.
Add the reserved crumble mixture on top, breaking it up into large chunks to give it a nice texture.
Bake for 55 minutes at 180°C/350°F.
The bars can be enjoyed after cooling to room temperature or can be allowed to cool in the fridge to make cutting easier.
