Place the farro in a bowl, and pour on enough hot water to cover by an inch. Let soak while you prepare the remaining ingredients. Drain.
Place the dried mushrooms in a large Pyrex measuring cup or bowl, and pour in 2 cups boiling water. Let sit 30 minutes.
Drain the mushrooms through a strainer set over a bowl and lined with cheesecloth or a paper towel. Squeeze the mushrooms over the strainer, then rinse in several changes of water to remove grit. Chop coarsely if the pieces are large and set aside. Add the broth from the mushrooms to the stock. You should have 6 cups (add water if necessary). Place in a saucepan, and bring to a simmer. Season with salt to taste.
Heat the oil over medium heat in a large, heavy nonstick skillet. Add the onion. Cook, stirring, until it begins to soften, about 3 minutes. Add the fresh mushrooms. Cook, stirring, until they begin to soften and sweat. Add salt to taste, the garlic and rosemary. Continue to cook, stirring often, until the mushrooms are tender, about 5 minutes. Add the farro and reconstituted dried mushrooms. Cook, stirring, until the grains of farro are separate and beginning to crackle, about 2 minutes. Stir in the wine and cook, stirring until the wine has been absorbed. Add all but about 1 cup of the stock, and bring to a simmer. Cover and simmer 50 minutes or until the farro is tender; some of the grains will be beginning to splay. Remove the lid, and stir vigorously from time to time. Taste and adjust seasoning. There should be some liquid remaining in the pot, but not too much. If the farro is submerged in stock, raise the heat and cook until there is just enough to moisten the grains, like a sauce. If there is not, stir in the remaining stock. If not serving right away, cover and let stand. Just before serving, bring back to a simmer, add the Parmesan, parsley and pepper, and stir together. Remove from heat and serve.