Heat a large pan of water, add the
potatoes, then cook for 8 mins until just
soft. Add the peas 1 min before the end
of cooking time. Drain, then set aside.
Meanwhile, heat the oil in a frying pan.
Fry the onion until soft and slightly
coloured. Add the curry paste and
mustard seeds, then fry for a few mins
more until the mixture smells fragrant.
Carefully stir in the potatoes and peas,
trying not to mash them. Add the lemon
juice and coriander, then leave to cool.
Heat oven to 200C/fan 180C/gas 6.
Unroll the pastry rectangle, place on
a floured surface with the long side
towards you and roll it out a little more
to make it into a square shape. Cut into
4 squares, then cut each one in half so
you have 8 long rectangles. Place 4 of
them onto a baking sheet, brush the
edges with beaten egg and place a
quarter of the filling down the centre
of each. Top with the remaining pastry,
then pinch the edges together to make
a sealed parcel. Brush with more egg,
then bake for 20 mins until puffed and
golden. If cooking from frozen, bake for
30 mins. Serve with fresh green salad
and a spoonful of chutney.