Heat the oven to 200C/fan 180C/gas 6.
Fry the beef in 1 tbsp olive oil in a large
non-stick pan, until browned. Add the onions,
carrots and celery, and fry until softened. Stir
in the tomato purée then sprinkle over the
flour and stir in well. Add the Worcestershire
sauce and stock, and simmer for 20 minutes
until sauce is reduced and thickened. Season.
Meanwhile boil potatoes until tender then
mash with the butter, cheddar, mustard and
a little salt. divide the beef mix between 4
dishes. Top with the mash, then bake for
25-30 minutes until golden and bubbling.