Heat the oil in a medium saucepan,
then soften the onion and carrots for
a few mins. When soft, turn up the heat,
crumble in the lamb and brown, tipping
off any excess fat. Add the tomato
purée and Worcestershire sauce, then
fry for a few mins. Pour over the stock,
bring to a simmer, then cover and
cook for 40 mins, uncovering halfway.
Meanwhile, heat the oven to 180C/
fan 160C/ gas 4, then make the mash.
Boil the potatoes in salted water for
10-15 mins until tender. Drain, then
mash with the butter and milk.
Put the mince into an ovenproof dish,
top with the mash and ruffle with a fork.
The pie can now be chilled and frozen
for up to a month. Bake for 20-25 mins
until the top is starting to colour and
the mince is bubbling through at the
edges. (To bake from frozen, cook at
160C/fan 140C/gas 3 for 1 hr-1 hr 20
mins until piping hot in the centre. Flash
under the grill to brown, if you like.)
Leave to stand for 5 mins before serving.