Ale and mushroom pie with champ

Preheat oven to 200ºC (400ºF, gas mark 6). Melt 50g of margarine in a large, non-stick frying pan (you may find it easier to do in two batches). Chop the bottom 7cm part of the spring onions roughly and sauté briefly. Save the tops as you will need them later. Add the sliced mushrooms to the pan. Continue to sauté for 5 mins until they start to colour, stirr to prevent sticking. Take off the heat and sprinkle the cornflour over. Put back on the hob, and add the yeast extract and 300ml of ale. Cook for a further 5 mins or until mushrooms begin to soften. Use more ale if the mixture seems too dry. Divide the pie mixture into 4 small soufflé/ceramic pie dishes. Cut out 4 circles of the pastry and place on top, leaving some room to rise. Brush with milk or soya milk and make a small hole in the top to let the steam escape. Bake for 20 mins until golden. For the champ, cut the potatoes into large chunks and boil until soft but not falling apart. Drain and empty back into the pan to dry slightly. Add the remaining 50g margarine and mash very well. Finely chop the remaining green part of the spring onions and add, with enough milk or soya milk, to make a smooth mash, and serve with the pie.