Bring 4 cups water and 1/2 teaspoon salt to a boil. Cook farro 10 minutes or until al dente. Strain and cool; set aside.
Place dried porcini mushrooms in 1 cup lukewarm water; let stand 10 minutes. Chop mushrooms, and reserve liquid.
Combine fresh mushrooms, 1/4 cup olive oil, remaining 1/2 teaspoon salt, and pepper in a medium bowl, and toss to coat. Place on a baking sheet; roast at 400° for 20 minutes or until golden, stirring twice.
Heat 1/4 cup olive oil in a Dutch oven over medium heat. Add onion and next 3 ingredients; cook until tender. Add bay leaf and next 3 ingredients. Stir in chopped hydrated porcini mushrooms, porcini liquid, and remaining 1 tablespoon olive oil. Cover, reduce heat to low, and cook 30 minutes or until cavolo nero is tender. Stir in farro and broth. Simmer, uncovered, 10 to 15 minutes or until almost all liquid has been absorbed. Fold in roasted mushrooms. Remove bay leaf.