Thinly slice 1 large leek, discarding any particularly thick, dark green leaves, and wash thoroughly. Put the sliced leek in a deep saucepan over a low heat with 30g of butter and cover with a lid. Let the leek cook in the butter for 10-15 minutes until they are softened. Don’t let it brown.
Stir 1 heaped tbsp of plain flour into the sliced leek, continue cooking for a couple of minutes, then pour in 250ml of double cream. Coarsely grate 100g of Caerphilly cheese into the leeks, season with 1 tbsp each of grain and smooth mustard, then a little salt and black pepper.
Heat an overhead grill. Place 4 rounds of thick sliced bread on one side, toast them under the grill then turn them over. Spoon the leek and cheese mixture over them and return to the grill. Cook until the leek and cheese has turned patchily golden. I like mine blistered dark brown here and there. Serves 2.
The sliced leeks can turn bitter if browned. To avoid them taking on any colour, I often put a piece of greaseproof paper, torn to fit, over them and then a lid. The paper encourages the leek to cook in its own steam rather than fry, resulting in soft green slices. I suggest you use a full-flavoured farmhouse cheese.
Onions and cheese make a fine topping for toast. After peeling, cut the onions in half and then into segments, letting them cook slowly in butter until they are truly soft and translucent. Then carry on as above, but with 1 tsp of chopped thyme leaves added. Pieces of bacon, crisped on the grill, then crumbled into the cheese and leek topping is a thoroughly good thing, as is a layer of air-dried ham placed under the filling before toasting.
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