Place 2 cups hot water and porcini mushrooms in a small bowl; cover and let stand 20 minutes or until tender. Drain mushrooms through a fine sieve over a bowl, reserving liquid. Coarsely chop mushrooms.
Heat oil in a large saucepan over medium-high heat. Add porcini mushrooms, cremini mushrooms, onion, and garlic to pan; sauté 6 minutes. Stir in farro; cook 1 minute, stirring occasionally. Add wine; cook 1 minute or until most of liquid evaporates. Add reserved mushroom liquid, thyme, salt, pepper, and broth; bring to a boil. Reduce heat, and simmer 45 minutes or until most of liquid evaporates, stirring occasionally. Remove from heat; stir in cheese.