Instructions: Trim the leeks, removing the leafy top and the bottom. Cut a cross into the tops and plunge into cold water to remove any soil from the vegetable. Simmer in water to cover along with 2 tsp lemon juice until the leeks are cooked

(about 30 minutes). Take care not to boil too agitatedly as the leeks will break up.

Meanwhile, make cheese sauce by melting the butter in a medium pan then stirring in the flour.

Allow to cook gently for 3 minutes.

Add the milk, a little at a time, stirring frequently.

Once thickened, add cheese, nutmeg, paprika and parsley (if using).

When cheese has melted and the sauce is smooth, remove from heat and stir in the egg yolk.

Drain leeks well and allow to cool a little before assembling the dish. In an ovenproof dish put a layer of mashed potato (if using).

Roll each leek in ham slices, cutting up the leeks into shorter lengths if they are too long.

Place in the oven proof dish and top with half the sauce.

Beat egg whites with remaining teaspoon of lemon juice until peaks form.

Fold remaining sauce into the egg whites.

Pour over other cheese.

Sprinkle with a little Parmesan cheese and a few breadcrumbs.

Cook in 190 C oven for 25 to 30 minutes until top is beautifully browned.

Leftover potential: Keeps two or three days in the refrigerator.

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