Preheat the oven to 180ºC / 350ºF / Gas Mark 4. Grease a large, ovenproof dish and reserve.
Bring a large saucepan of lightly salted water to the boil. Add the pasta, return to the boil
and cook for 8-10 minutes, or until tender but still firm to the bite. Drain well, return to the
saucepan, add 55g / 2 oz of the butter and toss well.
Spoon half the spaghetti into the prepared dish, cover with the strips of smoked salmon, then
top with the prawns. Pour over half the Bechamel Sauce and sprinkle with half the Parmesan. Add the
remaining spaghetti, cover with the remaining sauce and sprinkle with the remaining Parmesan. Dice
the remaining butter and dot it over the surface.
Bake in the preheated oven for 15 minutes, or until the top is golden. Serve immediately.