Leeks in a Welsh Cheese Sauce

For the Leek Gratin

2 large leeks
100g strong grated Welsh Snowdonia Cheddar
25g Welsh butter
25g Plain Flour
250ml milk

Trim the leeks, discarding the tough green ends and outer leaves. Cut the leek in half lengthwise, then slice into 1cm thick semi ring. Put in a colander and wash thoroughly. Put the leeks into a gratin dish.

Make the cheese sauce by melting the butter over a medium heat, then adding the flour. Cook for about a minute; gradually add the milk, stirring all the time till all the milk in incorporated and the sauce is thick and glossy. Cook for a couple of minutes, and then stir in all but 2 tablespoons of the grated cheese. Check and adjust the seasoning. Pour the sauce of the leeks and then sprinkle with the grated cheese.

Put some foil on the top and put in the oven with the lamb and potatoes for 60 minutes. When the lamb comes out take the foil off and brown at the same time as the potatoes until the cheese is browned and bubbling.