Place the farro in a bowl, and pour on enough hot water to cover by an inch. Let soak according to package instructions (some types of farro must be soaked overnight).
Place the dried mushrooms in a large bowl. Cover with 2 cups boiling water. Let sit 30 minutes.
Drain the mushrooms through a strainer set over a bowl and lined with a paper towel. Squeeze the mushrooms over the strainer, then rinse in several changes of water to remove grit. Chop coarsely. 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. Salt to taste.
Heat oil over medium heat in a large skillet. Add the onion. Cook, stirring, until it begins to soften, about three minutes.
Add the fresh mushrooms. Cook, stirring, until they begin to soften and sweat. Add salt to taste, garlic and rosemary. Continue to cook, stirring often, until the mushrooms are tender, about five minutes.
Add the farro and dried mushrooms. Cook, stirring, until the grains of farro are separate and beginning to crackle, about two 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 until the farro is tender, about 50 minutes. 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. Add the Parmesan, parsley and fresh ground pepper to taste, and stir together. Remove from the heat and serve.