In a small bowl, soak the porcini mushrooms in 1 1/2 cups hot water until softened, 15 minutes.
In a large skillet, melt 1 tablespoon of the butter over medium-high heat. Add one-third of the assorted mushrooms, season with salt and pepper and cook, stirring occasionally, 4 minutes, or until lightly browned. Remove mushrooms to a plate and repeat twice with remaining mushrooms. Return all cooked mushrooms to skillet.
Drain porcini mushrooms, reserving liquid, and coarsely chop. Add porcini, shallot and garlic to mushrooms and cook over moderate heat, stirring, 3 minutes. Strain porcini liquid over mushroom mixture, stopping before adding any grit or sand. Boil over high heat 4 minutes, or until reduced by half. Stir in parsley and season with salt and pepper. Remove from heat and fold in remaining 1 tablespoon butter.