Put the dried porcini (if using) into a bowl and cover with warm water. Leave for 30 minutes then drain. Keep the water. Peel the garlic. Wash, peel and cut the leek into rounds. Then clean the fresh mushrooms (if using) and remove any dirt with a slightly damp cloth. Cut the mushrooms (porcini or fresh) into small pieces. Remove the casing from the sausage and chop the meat into small pieces.

Put the extra virgin olive oil and the whole garlic into a skillet or deep frying pan. Heat the oil and let the garlic soften slightly. Add the leeks and saute over a low heat for at least 10 minutes. When the leeks are soft, add the sausage meat to the pan. Let it brown over a medium heat, turning it often. Then add the white wine.

Let the alcohol evaporate for a few moments, then add the tomato paste and the mushrooms. Cook over a medium heat for 10 minutes, then add salt and pepper and remove the clove of garlic. If you have used dried porcini you can add a little of the soaking water at this point. When the mixture in the pan is quite dry/reduced, then turn off the heat and let it cool.

Melt the butter in a saucepan, then add the all-purpose flour (sifted). Stir continuously until a paste forms. This is called a roux. Add the milk to the roux a little at a time, stirring continuously, until you get a smooth sauce. Add ⅓ of the grated cheese and continue stirring until the cheese has melted and the sauce has thickened. Season with a pinch or two of salt, black pepper and freshly grated nutmeg. You don’t want the sauce to be too thick so add more milk if necessary.

If using ready made béchamel heat it in a pan and add ⅓ of the grated cheese to it. Turn off once cheese has melted. If too thick add some milk.

Put a pot of water onto boil for the pasta. Add salt once it starts to boil and bring to the boil again. Add the pasta and a teaspoon of olive oil to the water. Cook the pasta a couple of minutes less than al dente according to the instructions on the packet. Drain the pasta and run cold water over it to stop it cooking further.

Put the drained ricotta into a bowl, add ⅓ of the Parmigiano cheese and the cooled mixture of leeks, sausage and mushrooms. Stir and season with salt and pepper if necessary. Using an immersion blender, reduce the filling to a pesto type sauce. You can also just chop it into smaller pieces with a sharp knife.

Put a little béchamel sauce into the bottom of a round oven dish. I used a terracotta one. Fill the dish with paccheri tubes standing vertically. Then fill each pasta tube with the filling using a teaspoon or a pastry bag. I found it easier to lift each pasta tube out of the dish, fill from both sides and replace.

Once you have filled all the paccheri, pour the remaining béchamel over the pasta and sprinkle the top with the rest of the parmigiano. Cook the stuffed paccheri in a preheated oven at 180 °c for about 20 minutes + 5 minutes under the grill to brown the surface (if necessary). Remove the stuffed baked paccheri from the oven. Let it rest for 5 minutes and then serve.