Preheat the oven to 200°C / 400°F / Gas mark 6.
In a saucepan, add 600ml of milk with 6 peppercorns, 1 bay leaf and a slice of onion and heat.
Place the butter in a heavy saucepan and melt until foaming, add the flour and cook for 3 minutes stirring continuously.
Remove from heat and whisk in the milk.
Return to the heat, bring to the boil whilst whisking the sauce and simmer until thickened and smooth.
Add the grated cheese and stir until melted in the sauce. Season with salt and pepper.
Place ⅓ of the cheese sauce in a small bowl and add the seafood in to the saucepan with the remaining ⅔ and cook for about 5 minutes.
Cover with cling film or a plate and remove from the heat.
Place the spinach in a bowl and wash thoroughly, drain then cook in a saucepan, with lid on and until the spinach has wilted.
Remove from heat, season with nutmeg, salt and pepper.
Using an oven proof dish, place lasagne sheets on the bottom, add ½ the seafood mixture on top, a layer of ½ the spinach, layer of pasta, seafood, spinach, and pasta on top.
Then add the remaining cheese sauce and sprinkle on the extra cheese.
Place in the oven and cook for approximately 30-40 minutes or until golden bubbly and cooked through.