1. Prepare the béchamel. In a saucepan, melt 40 g of butter over medium heat; add the flour, stirring with the whisk. Then pour the cold milk all at once, stirring constantly until it begins to boil. Add salt, some nutmeg, pepper and reduce the intensity of the flame and cook stirring occasionally until it thickens. Remove from heat, adjust the salt if necessary.
If the béchamel went too firm, add a little milk. If it went too liquid, place on the heat adding a pinch of floured butter.
2. Boil the conchiglioni pasta in abundant salted water, leaving them still “al dente”. Drain and cool them, quickly, in cold water, drain well and season with a drizzle of extra virgin olive oil to prevent them from sticking.
3. Prepare the filling: mix the ricotta with the pesto, 50 grams of grated Parmesan and the marjoram chopped, season with salt.
4. Take the baking pan, one large or 4 one portion, and lightly butter them. Sprinkle the bottom with a little of béchamel. With the help of a teaspoon, fill all the conchiglioni with the filling, gradually placing them in the pan. Fill the baking pan with the remaining béchamel, add the Parmesan and a few remaining butter flakes.
Cook the conchiglioni at 200°C for about 20 minutes or until the surface is golden and a bit crunchy. Serve immediately.