Combine the porcini mushrooms and boiling water in a bowl; cover and let stand 30 minutes. Drain porcini mushrooms in a colander over a bowl, reserving 1 cup liquid. Rinse and chop porcini mushrooms; set aside.
Melt butter in a large saucepan over medium-high heat. Add shiitake mushrooms, shallots, and garlic; sauté 6 minutes or until tender. Stir in the porcini mushrooms, 1 cup reserved liquid, potato, and next 4 ingredients (potato through pepper). Bring to a boil; cover, reduce heat, and simmer 10 minutes or until potato is tender. Stir in Smoked Gouda Cheese Sauce; cook 5 minutes or until thoroughly heated. Stir in sherry.