Cook the spinach with a little water and a pinch of salt. Once cooked, drain and chop with a knife.
Heat a saucepan with water and when it bubbles add a teaspoon of oil and a handful of salt.
Blanch the pasta dipping one sheet at a time for about 1 minute, then take it with a skimmer and lay it on a cloth towel so that it dries. Do this for all the sheets.
Mix the ricotta with spinach in a bowl then mix in the Parmesan and stir it all up to create a homogeneous filling.
Butter the surface of the lasagna dish and add ingredients as follows: spread the ricotta mix until it covers the entire surface followed by two ladles of bechamel, a layer of sheets of pasta. Continue this sequence for three other layers until the last that will be made only of white sauce, Parmesan cheese and butter flakes.
Put the dish in the preheated oven and bake at 180 degrees for about 40 minutes.