Wash lemon hot, grate dry and finely grate half of the peel. Wash and clean sorrel and put 2 nice leaves aside.
Heat butter in a frying pan. Add sorrel and let it collapse for about 3 minutes. Season sorrel with salt, pepper and nutmeg and pour into a bowl. Leave to cool. Squeeze sorrel and chop coarsely.
Mix crème fraîche, sorrel and lemon peel and season again. Grease 4 ovenproof moulds (200 ml each) and distribute the sorrel. Press a depression in the middle and beat in 1 egg at a time.
Half fill the fat pan of the oven with hot water and place the dish on top. Cook the tins in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 10-15 minutes.
Cut remaining sorrel leaves into thin strips. Remove from the oven, garnish with sorrel and trout caviar. Delicious with baguette.