British
Boil the potatoes until tender, then mash with the butter and milk and season.
Fry the onion and carrots in the oil until softened, then add the lamb mince and brown well.
Stir in the tomato puree and Worcestershire sauce, pour in the stock and simmer for 20 minutes until thickened.
Add the peas, then spoon the meat into an ovenproof dish.
Spread the mash evenly over the top and rough up the surface with a fork.
Bake at 200C for 25 minutes until golden and bubbling at the edges.