We start with the shrimp: thaw the shrimp completely, to room temperature; one way is to leave the shrimp in a colander in cold water. Another method would be to take them from the freezer the night before and put them in the refrigerator.
Soak the mushrooms in water: place the mushrooms in a bowl and pour warm water over them. Allow them to soak for one hour.
Prepare the green beans: peel the beans, wash them, steam-cook them, let them cool down and mash them using a food mill.
Sauté the mushrooms: chop the onion and sauté over medium-low heat in a tablespoon of oil. Meanwhile, squeeze the mushrooms. If they are too big cut in smaller pieces. Mix in the the onions, cook everything for a minute, stirring, and then pour a part of their soaking water and a little bit of hot water, just enough to cover the vegetables. Add salt, add the bay leaves and simmer for 15-20 minutes. Cook to reduce the liquid and then add the parsley just before turning off the heat. Add more hot water if necessary. If you like you can use vegetable broth instead of water.
Cook the potatoes: in a nonstick pan put a tablespoon of olive oil and the potatoes previously cut into small pieces. Sprinkle the dried rosemary over and cook over medium-low heat, stirring often. Cook the potatoes until they are golden; this takes about 15 minutes. Season with salt and stir with the heat off.
Cook the pasta: cook the pasta al dente in salted water into which you wil have added the rest of the water from the mushrooms. Be careful not to add any excess dirt from the mushrooms: filter the water through a tightly woven cotton cloth. A colander is not enough. Drain the pasta and pass it under cold running water to stop the pasta cooking process, drain well again.
The last step: transfer the pasta in a large bowl. Add the mushrooms, the potatoes, a tablespoon of olive oil and the chives. Mix gently and set aside. In the skillet where you cooked the potatoes or mushrooms cook the pureed beans, stirring often. No need to add more oil. Season with salt and add the shrimp two minutes before turning off the stove. Allow to Cool. Pour into bowl.
Combine with some freshly chopped basil leaves, if you like. Stir gently to mix all ingredients, taste and adjust salt if necessary. Wait at least 30 minutes before serving.