Cook the potatoes in boiling, salted
water for 5-8 mins until tender, but still
holding their shape. Meanwhile, melt the
butter in a large saucepan. Add the leeks
and thyme and soften for 10-12 mins.
Drain potatoes and add to the leeks with
the mustard and plenty of seasoning. Stir
in the cream and leave to cool a little.
Heat oven to 180C/160C fan/gas 4.
On a floured surface, roll out the pastry
to the thickness of a £1 coin. Use a side
plate or a bowl as a template to cut
out 6 x 15cm circles. Mix the cheese
with the leek mixture and pile a mound
of the mix onto the centre of each pastry
circle. Brush around edges with a little
egg, then bring edges together and
crimp with your fingers to seal.
Place pasties on a baking tray
lined with baking parchment, brush
with the remaining egg and bake
for 40-45 mins until golden brown.
Serve warm or leave to cool.