Toss the meat in the flour to coat. Working in batches, heat the oil in a large, deep casserole, add the meat and cook, stirring, to brown evenly. Remove to a plate. Add the shallots and cook for 5-8 minutes, until lightly browned. Add the reserved meat and the mushrooms.
Add the ale, stock, sugar, mustard and bouquet garni and bring slowly to a simmer, covered, then cook at a slow simmer for about 1 hour.
Using a slotted spoon, remove the meat and vegetables to a pie dish, about 28 x 23cm (11 x 9in). Boil the cooking liquid until reduced to 500ml (18fl oz). Taste and adjust the seasoning, adding a little more sugar if needed.
Meanwhile, cook the vegetables for 2-3 minutes, in batches, in boiling, salted water. Transfer them to the pie dish and mix. Strain the reduced cooking liquid, discarding the bouquet garni, then pour it over the filling. Heat the oven to 180°C (350°F, gas mark 4).
Brush the rim of the pie dish with some of the beaten egg. Cut the whole filo sheets to cover the top of the pie dish, and press them onto the rim. Lightly brush the remaining filo with oil and scrunch lightly to give a crumpled effect. Place them over the pie to cover completely. Cook for 20 minutes until the top is golden, and the contents hot.
i made this pie with shortcrust pastry made with half butter and half lard. i used sop bought bouquet garni and replaced the dijon mustard with 2 teaspoons of dried english mustard - 17 Jun 2010