1. Soak farro overnight in water to cover; drain.

2. In a small bowl, pour boiling water over porcini; let stand 5 minutes. Drain, reserving liquid. Chop porcini.

3. In a medium saucepan, combine farro, broth, and porcini liquid. Bring to a boil, then reduce to a simmer, cover, and cook until almost tender, about 45 minutes.

4. Meanwhile, melt butter in a large skillet over high. Add onion, garlic, and porcini mushrooms and cook, stirring frequently, until onion is translucent, about 4 minutes. Add wild mushrooms and cook, stirring occasionally, until mushrooms have released liquid and begun to brown, 6 to 7 minutes. Season with salt and pepper. Stir in sherry; cook until evaporated, about 1 minute.

5. Stir mushroom mixture into soup; cook, partially covered, until farro is tender, about 15 minutes. Season with vinegar, salt, and pepper. Serve, sprinkled with dill.