To make the pâté, remove as many of the bones as possible from the kippers and skin each fillet (the skin will pull off easily). Cut the meat into small pieces along with the white fish and blend in a food processor or blender until smooth. Add the salt and the white of 1 egg, and process again to beat in well. Rub the mixture through a sieve into a bowl set over crushed ice. Stir in the remaining egg and the egg yolk together with the white wine and mix in well. Gradually add the cream but do not overwork the mixture. Butter 6 oval or round moulds (7.5 x 4 cm/3 x l½ inches), half fill each mould with the mixture, then firmly bang each mould a few times on a firm surface to remove any air bubbles. Finish filling each mould with the pâté, and again bang each one on a firm surface. Cover the moulds with buttered foil and cook in the oven for 18 minutes.
For the sauce, bring the fish stock to the boil and reduce over a high heat until it is thick and syrupy. Add the shallots, the lemon juice and the cream, and return to the boil. Once the sauce is boiling, reduce the heat to very low and gradually whisk in the butter. Continue whisking until all the butter has melted. Do not allow the sauce to boil once you have started to add the butter. If you need to keep the sauce hot for a few minutes, put the sauce in a bain-marie over a very low heat.