Heat oil in a large heatproof casserole and add leeks, carrot, parsnip and celery. Cook stirring occasionally for 7-8 minutes.
Toss lamb in flour, shaking off any excess. Add flour-coated lamb to vegetables and cook, stirring, for 5 minutes.
Add red wine, rosemary, tomato paste, chopped tomatoes and stock and bring to the boil. reduce heat and simmer for five minutes, stirring occasionally.
Cover and cook in oven at 170°c (fan) for one hour and 45 minutes or util lamb is tender; set aside to cool. Season to taste with salt and pepper.
To assemble the pie, preheat oven to 180°c (fan). Transfer the lamb to a large ceramic dish - it should fill the dish almost to the top. Drape the pastry sheets over the pie dish, layering together to join if necessary. Use a fork to prick the top a couple of times.
Brush the top with beaten egg. Bake for 30-40 minutes or until golden and risen.