Layer the potatoes with the roughly chopped leeks, cashew cream, salt, pepper and rosemary. Keep layering until the dish is full. The last layer should of potatoes and some cream. Cover and bake for 1 hour.
Make oats crumble by mixing the oats with some water, salt and herbs and baking at the same temperature for one hour.
Sprinkle the dish with the oats crumble.