1. Place the haddock in a food processor with the crabmeat, egg white, 1 teaspoon lemon juice and anchovy essence and blend until smooth. Taste and add pepper and a little salt if necessary. Chill the mixture for 30 minutes.
2. Gently heat the oil in a saucepan, add the rice and toss until thoroughly coated. Add the water and simmer uncovered until it has been absorbed. Remove from the heat and leave to cool. The rice will only be partially cooked.
3. Wash the spinach, trim the stalks back to the leafy parts and place in a large bowl; pour boiling water over to cover and leave to stand for 3-4 minutes. Drain and dry thoroughly with paper towels.
4. Lightly whip the cream and combine it with the fish mixture, folding in the partially cooked rice at the same time.
5. Place a dollop of the mixture on a spinach leaf, fold in the sides and, starting with the stalk end, roll the leaf up to form a compact parcel. Prepare the rest of the spinach leaves in the same way. Pack the stuffed leaves into a greased gratin dish, pour over the tablespoon of lemon juice mixed with a tablespoon of water and cover. Place in a roasting tin half-filled with water and bake in a preheated oven for about 1 hour. Allow to cool completely, with the lid on.
6. To serve, arrange the parcels on a platter.