Heat half the oil in a non-stick frying pan and cook the mince over a high heat, breaking up
with a wooden spoon, until well browned. Remove the mince from the pan with a slotted spoon, pour
away any fat and wipe the pan with kitchen paper.
Add the remaining oil to the frying pan and cook the leek, onion, carrots and celery for 15
minutes until soft. Return the mince to the pan and add the mushrooms, tomatoes, thyme and water.
Season to taste with salt and pepper and leave to simmer for 40 minutes, stirring occasionally.
Meanwhile, preheat the oven to 180ºC / 350ºF / Gas Mark 4. Mix the 2 mashes of potatoes with
half the milk and half the butter in a bowl and season to taste with salt and pepper.
Spoon the meat sauce into a baking dish and top with the potato mixture. Brush with the
remaining milk and dot with the remaining butter. Bake in the preheated oven for 35 minutes until
the topping is brown and crisp.