First a bit about using dried porcini mushrooms.

To reconstitute the mushrooms:

• The best way to reconstitute dried mushrooms is to simply soak them in water for 30 minutes. If you want to use the mushrooms themselves, use room temperature water. If you primarily want the liquid, use boiling water. (Cooler water extracts less of the flavor from the mushrooms.)
• Once they’ve soaked, taste a mushroom. If you detect any grittiness, you'll need to rinse the mushrooms in a strainer under running water, to make sure all the grit is gone.
• Much of the mushroom’s grit is released into the soaking water and will have fallen to the bottom of the bowl. You do not want to add this grit to your dish so either pour it carefully out, leaving the heavier grit in the bowl or strain your broth through a coffee filter or paper towel. 

PORCINI FARROTTO

• 3 cups chicken or vegetable stock or water
• 1 ounce dried porcini 
• 1/4 cup extra virgin olive oil
• 1 medium yellow onion, finely diced
• 1/2 cup dry white wine (or dry sherry)
• 2 cups farro 
• 1/2 cup Parmesan, finely grated
• 1 tablespoon unsalted butter
• salt & pepper

In a small bowl, combine dried porcini and 3 cups of hot water and let rehydrate until mushrooms are soft and pliable, about 30 minutes. Drain mushrooms (reserving the soaking liquid), rinse if needed, and chop into small pieces. Set aside.

In a medium saucepan, combine the reserved mushroom soaking liquid (be sure to leave any grit in the bottom of the bowl) with the stock and bring to a simmer over medium heat. Reduce heat to low and keep warm.

Heat olive oil in a large heavy-bottomed pot over medium high heat. Add onion and sauté until translucent, about 5 minutes. Add farro and toast for a couple minutes. Add white wine and stir until farro has absorbed liquid. Add reserved chopped mushrooms and 1 cup of hot stock stirring until the liquid has been absorbed once again. Continue adding stock, making sure most of the liquid is absorbed before adding more and stirring frequently until farro is tender, about 30 minutes. You may not need all the stock.

Remove from the heat, add grated Parmesan and butter and stir vigorously to make it even creamier. Season with salt and pepper to taste.