Chop the smoked salmon into very small pieces.
Skin the trout and remove the flesh from the bones.
Pound the trout flesh and salmon to a pulp and gradually work in the butter until you have a smooth paste.
Add the chopped onion and mix thoroughly.
Season with salt and pepper to taste and add a little grated nutmeg.
Press the mixture into 2 individual ramekin dishes, cover and chill thoroughly for 3-5 hours.
Serve the pate garnished with sprigs of watercress, offer lemon quarters to squeeze over the pate and hot toast to eat with it.