Baked Penne with Double Mushroom Sauce

Rinse and drain common mushrooms. Trim and discard discolored stem ends; cut mushrooms wider than 1 inch in half lengthwise through caps. In a 5- to 6-quart pan, combine mushrooms, onions, garlic, and 1/2 cup broth. Stir often over high heat until liquid has evaporated and mushrooms begin to brown, about 20 minutes. Add 11/2 cups broth and stir often until liquid has evaporated, 12 to 15 minutes longer. Meanwhile, in a bowl, pour 2 cups boiling water over porcini mushrooms; let stand until mushrooms are limp, about 10 minutes. Squeeze porcinis in water to release grit, then lift out, squeeze dry, and chop. Slowly pour out 13/4 cups soaking water, leaving sediment behind, and reserve; discard remainder. In another bowl, blend remaining 2 cups broth with cornstarch. Add chopped porcinis, soaking liquid, vermouth, and thyme to pan with common mushrooms. Mix in cornstarch mixture and stir until boiling. Remove from heat. In another 5- to 6-quart pan over high heat, bring 3 quarts water to a boil. Add pasta and stir occasionally until tender to bite, about 12 minutes. Drain. Mix pasta with mushroom sauce; add mozzarella cheese and stir to blend. Pour pasta mixture into a shallow 3-quart casserole (about 9 by 13 in.). Bake, covered, in a 350 degrees oven until sauce begins to bubble, about 25 minute (1 to 11/4 hours if chilled). Uncover, sprinkle evenly with parmesan cheese, and bake about 5 minutes longer. Let stand 10 minutes. Sprinkle with parsley. Spoon out portions. Add salt and pepper to taste.