60g butter or margarine
Salt and pepper, to taste
Peel the swede and cut it into large chunks. Place the swede in a steamer basket over a pan of boiling water, then cook it for about 30 minutes until soft. Preheat the oven to 200C/gas mark 6.
Meanwhile, trim and slice your leeks, and rinse thoroughly in cold running water. Melt the butter or margarine in a pan, add the leeks and cook for 20 minutes or so until they are totally tender.
When the swede is soft, crush it with a fork, vegetable masher or wooden spoon, and season generously with salt and black pepper.
Fold the cooked leeks and the butter they have been cooked in into the mashed swede, then spoon them into an ovenproof dish. Bake for about 35-40 minutes, until the top is lightly crisp.