Combine boiling water and porcini mushrooms in a bowl; cover and let stand for 30 minutes. Drain. Rinse and coarsely chop porcini mushrooms.
Heat oil in a medium skillet over medium-high heat. Add prosciutto, and sauté 1 minute. Add onion; sauté for 3 minutes or until tender. Stir in the porcini mushrooms, cremini mushrooms, and next 4 ingredients (cremini mushrooms through garlic); cook 4 minutes or until browned, stirring frequently. Stir in broth and wine, scraping the pan to loosen browned bits.
Bring to a boil; cook for 3 minutes. Combine the cornstarch and 1 tablespoon water in a small bowl. Add cornstarch mixture to pan; bring to a boil. Cook 1 minute, stirring constantly. Add pasta, tossing to coat.