The first thing to do is to make a thick
white sauce that will be the base of
the turnover filling. Bring the milk to a
simmer, then add the butter and flour
paste. Whisk the paste into the simmering
milk and allow it to boil for 3-4 mins,
whisking gently all the time to prevent
it from catching. You should now have a
very thick white sauce. Cool the sauce in
a bowl. Fry the mushrooms in the oil for
3-5 mins until golden, then leave to cool.
Place the ham, cheese and mushrooms
into a bowl, then gradually add the white
sauce until everything is well coated.
Finally, add the herbs.
Roll out the pastry on a floured surface
to about the thickness of a £1 coin and
cut out 4 saucer-size rounds (about
18cm wide), re-rolling the trimmings if
you need to. Brush the edges of each
round with beaten egg. Spoon the
mixture onto 1 side of each round, then
fold over and seal the edges well. The
turnovers can now be frozen for up to
1 month. Brush the turnover with the
remaining egg, then chill for 30 mins.
Heat oven to 200C/180C fan/gas 6.
Place the turnovers on a baking sheet
and bake for about 35 mins until puffed
up and golden. Leave to cool slightly
and enjoy warm.