Let's start with the béchamel sauce: pour the milk into a saucepan, flavor it with the nutmeg and a pinch of salt and let it heat over low heat. Meanwhile, put the butter in another saucepan and let it melt on low heat, then turn off the heat and add the flour all at once, stirring with a whisk to avoid the formation of lumps.
Turn the heat back on low heat and continue stirring until the flour and butter mixture becomes golden. Pour a little 'hot milk into the saucepan and add the rest of the milk and mix with the whisk until the cream has reached a fairly fluid consistency.
Take a rectangular pan, pour a ladle of béchamel on the bottom and spread the whole surface; lay down 3 sheets of lasagne. Pour another ladle of béchamel to cover the sheets, add a handful of previously washed and dried spinach and cover with the slices of smoked salmon with a sprig of dill and a ground pepper. Repeat the layers until the ingredients run out.
Once completed, cook the lasagna in a preheated oven at 180 ° for about 40 minutes, positioning the pan on the central shelf, until they are golden on the surface.