Heat the oven 180 degrees C
On a baking tray add some olive oil & sweet potatoes, bake until tender – remove & place into a bowl
Remove the leaves from the kale stems & roughly chop them.
Heat the oil the butter in a pan, then fry the onion, kale & mushrooms for about 10 mins until soft & the water from the pan has evaporated - Add this to a large bowl
Add the crème fraîche, parmesan, 100g of the gruyere cheese and the nutmeg to the bowl with everything & stir well – season with a good amount of salt & pepper – allow to cool slightly
Melt the butter. Lay a sheet of filo on a large baking sheet
With the long side of the baking sheet towards you, spoon the filling along the pastry, about 4cm in from the edge. Sprinkle the remaining gruyere cheese on top.
Carefully roll the filo and the stuffing into a fat log shape and tuck the ends underneath to seal
Brush the strudel with more butter, scatter over the poppy seeds and bake for 25 mins until golden brown