Heat oven to 200C/180C fan/gas 6.
Put the leeks and stock into a large pan,
then cover and cook for 5-8 mins until
starting to soften. Add the mushrooms,
cover again and cook for 3 mins, then
remove the lid and continue to cook
until the juices have evaporated. Tip the
veg onto a large plate to cool slightly.
For each strudel, lightly brush half
of each filo sheet with some olive oil.
Fold the un-brushed side over to make
a smaller sheet, 2 layers thick. Brush
the edges with a little more oil, then
spoon a quarter of the veg along one
edge. Crumble over a quarter of the
cheese, fold over the pastry edges,
then roll up to seal in the filling.
Put the strudels on a baking tray,
brush with any remaining oil and scatter
over the poppy seeds. Bake for 25 mins
until crisp and golden brown.