You just want it to cool a bit before layering it into the crumble bars. Add the oats, almonds, chia seeds, brown sugar and cinnamon to a large bowl. Mix to combine the dry ingredients.

Add the shelled pistachios and blitz again until the nuts are roughly chopped and the crumble has a light green hue. Tip the frozen mixed berries into a medium-sized round or square baking dish ...