Wide flat noodles are my preferred pasta shape with this smooth mushroom sauce. Often pappardelle or tagliatelle are hard to find so penne is a good substitute. If you can get fresh pasta go for it, but make sure you time the pasta to reach just shy of al dente when the sauce is done cooking. Fresh pasta is best eaten right after it is cooked.
This recipe is adapted from Lidia's Mastering the Art of Italian Cuisine by Lidia Matticchio Bastianich and Tanya Bastianich Manuali, Tagliatelle with Mushroom Sauce.
Add the minced leeks, garlic, minced reconstituted porcini mushrooms, half the minced rosemary, Kosher salt and fresh ground black pepper then stir to coat the vegetables. Cook until the leeks are soft about 5 minutes. Push aside the vegetables to uncover the hot spot of your pan and add the tomato paste to toast it over the hot spot for about a minute. Mix the tomato paste with the vegetables and cook for 4 minutes. Add all liquids, 1. 5 cups (375 ml) broth (combined with or without mushroom water) plus the sherry, and the butter. Turn down the heat to medium and simmer the mushroom sauce until the butter is melted and incorporated into the sauce, about 5 minutes. Taste and add more salt and pepper if needed.
Dried porcini powder is another way to get earthy mushroom flavor when cooking with cultivated mushrooms. Start with 1 teaspoon. Taste, then adjust with more if needed.