Remove the heart each bunch of spinach, do not discard the other leaves, which can be used for soup or risotto; wash the hearts well, drain them and once delicately dried, finely chop, but not too finely, put them in a colander to allow them to drain more water.Bring to the boil of pan with plenty of water to cook the pasta. Then preheat the oven at 200 °C. In the meanwhile place the ricotta in a bowl and dilute it with enough cream to reach the same consistency of bèchamel, season with a pinch of nutmeg, add the spinach, previously sautéd in a pan to allow it to dry properly, then add the salt to taste.Salt the pasta water, and once it boils again toss it in the pan and boil for a few minutes. Drain it al dente, arrange it in a well greased Pyrex, add some butter, keeping a knob of it aside.Cover it evenly with the sauce, sprinkle it with cheese and butter flakes. Put the dish in the oven for about 10 minutes until the top is a golden crust. Use the Pyrex to serve the pasta.