Heat oven to 200C/180C fan/gas 6. Fry
the sausages in a large frying pan until
browned all over, remove and set aside.
Remove most of the fat left in the pan,
then add leeks and soften for 8-10 mins. Add the peeled apple slices and cook for
1 min more. Stir in the flour, followed by
the mustard. Pour over the stock and
bubble for 2 mins to make a sauce.
Chop the sausages into chunks and stir
into the pan. Then, tip everything into
a large ovenproof dish. Top with the
pastry, trimming off any excess and glaze
with the egg. Bake for 25 mins until golden.