Steam 1kg (2¼lb) leeks for 5-10 minutes until just tender.
Make the cheese sauce
Melt 25g (1oz) butter in a small saucepan and stir in 25g (1oz) flour. Cook the flour over a low heat for about 1 minute, then remove from the heat.
Gradually add 300ml (½pt) milk while stirring well. Return to a low heat and keep stirring until the sauce thickens.
Crumble most of the 125g (5oz) cheese into the pan and continue to cook until the cheese has melted, stirring constantly
Season to taste with salt, pepper, and a little nutmeg.
To complete
Drain the leeks well and place in a shallow ovenproof dish and spoon the cheese sauce over the leeks.
Sprinkle 25g (1oz) breadcrumbs over the surface of the sauce, then sprinkle over the remaining cheese. Dot the remaining butter over the top of the dish and brown under a preheated grill until golden.
Notes
Cook' NotesTo prepare aheadPrepare the dish up until the end of step 5. Allow to cool then cover and chill until required. To serve bake in the oven at 190℃ (170℃ fan)/375°F/gas mark 5 for about 30 minutes or until the leeks are piping hot and the top is crisp and golden.To make breadcrumbsThe term "fresh breadcrumbs" is a bit of a misnomer since they are best made using bread that is beginning to go stale. To make crumbs remove crusts (if tough) tear the bread into pieces and add to the food processor and blitz until coarse crumbs form. . If you don't have stale bread, you can toast pieces in a warm oven for about 20 minutes until they are dried out.Store: Leftovers can be stored covered in the refrigerator for up to 2 days.Freeze: Not suitable for freezing