For the salmon mousse, cut the salmon into small pieces and purée in a blender or food processor together with the salt until smooth. Add the egg white and blend for a few seconds more or until it is well mixed in. Remove from the blender and rub the mixture through a sieve to remove any sinews – only by doing this can you be sure of a really fine texture. Set the bowl on crushed ice and gradually add two-thirds of the cream, followed by the vermouth and seasoning. Test the mousse. It should be soft and not rubbery, but should still hold together and not break up. Keep adding cream and testing until you obtain the right consistency.
To make the turbot mousse, follow the same steps as for the salmon mousse, adding the egg yolk and sherry together at the end.
The herb mousse is again made in exactly the same way as the other two mousses. When the mousse is made, add the mixed herbs.
To assemble the terrine, blanch the spinach leaves in boiling salted water for a couple of seconds and then refresh in iced water. Lay them out on a cloth to drain. Butter a
Place each mousse into a separate piping bag. Taking the salmon mousse, pipe a line of mousse along one edge of the terrine; this should go the full length and be about 2 cm/¾ inch wide. Next pipe in the turbot mousse, laying 1 line of mousse on top of the salmon mousse and 2 lines on top of each other next to it (the idea is to create a rainbow effect, with about 5 mm/
The terrine needs to be cooked in a bath of water or bain-marie to prevent it burning around the sides. Bring to the boil a tray containing sufficient water to come three-quarters of the way up the terrine. Put in the terrine and place in the oven for 45 minutes. After 25 minutes, remove the lid but leave the foil on. To test whether or not the terrine is cooked, pierce through the centre of the terrine with a trussing or darning needle. Hold it there for a couple of seconds, remove and hold it to your top lip. If it is warm in the centre, it is ready; if not, give it another 5 minutes and then try again. When cooked, remove the terrine from the tray and allow to go cold at room temperature.