Cook the swede and potatoes in a pan
of boiling salted water for 10 mins until
tender, then drain and set aside.
Heat oven to 200C/180C fan/gas 6.
Heat the oil in a large frying pan over
a low heat. Add the onion and carrots,
and gently fry for 5 mins. Add the
mushrooms, increase the heat to
medium and cook for a further 5 mins.
Tip the vegetables into a bowl.
Add the mince to the frying pan and
cook until browned. Pour away any
excess fat. Add the vegetables (not
the swede and potatoes), tomatoes and
tomato purée, cover and simmer for
15 mins, topping up with a little water
if the mince looks a bit dry.
When the swede and potatoes are cool
enough to handle, coarsely grate; then
toss in the melted butter and season.
Tip the mince mixture into a deep
ovenproof dish, top with the grated
swede and potatoes, then put in the
oven and cook for 40 mins.