Separate 1 egg. Brush 4 ovenproofs dishes with egg yolk. Place on a baking tray. Preheat the oven to 180°C (160°C fan, gas 4).
Wash the leeks, halve lengthways, cut into 4-5 cm pieces, then into fine strips.
In a hot pan, melt the butter and fry the leeks until softened. Chop the salmon into pieces. Allow the leeks to cool, add the salmon, chives and cream.
Mix well and season with salt, pepper and nutmeg.
Spoon into the dishes until about three-quarters full.
Place 1 beaten egg on each.
Pour over the remaining egg white, sprinkle with cheese and bake in the oven for 20 minutes. Serve sprinkled with chives.