Fry the onion, carrots and celery in the oil in a large frying pan until softened.
Add the mince, increase heat and cook for 5 mins or until well browned. Stir in the tomato pure, Worcestershire sauce and stock. Simmer for 5 mins until the sauce has thickened slightly. Cool for 10 mins.
Heat oven to 200C/180C fan/gas
Spoon the mixture into 4 individual pie dishes or one large dish.
Brush the dish rims with egg, then lay the pastry on top and trim. Seal edges with a fork and brush the pastry with more egg. Poke a little hole in the top and cook for 25-30 mins or until the pastry is golden and risen.
Meanwhile, cook the peas in boiling water, then drain and mash with the mint sauce.