Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
     1/2  ounce         dried porcini mushrooms -- - rinsed
     1/2  cup           hot water
   2      medium        shallots
   2      pounds        baking potatoes -- - (preferably
                        -- idaho)
                        peeled -- halved lengthwise
   1 1/2  tablespoons   olive oil
     2/3  cup           whipping cream
     2/3  cup           milk
     1/2  teaspoon      salt
                        freshly ground pepper
   3      tablespoons   whipping cream

Preparation:

Soak porcini in hot water 1-1/2 hours. Strain through paper towels; reserve liquid. Rinse porcini; squeeze dry. Discard any hard stems. Cut into strips. Preheat oven to 325 F. Generously butter 2-quart gratin dish. Mince shallots. Slice potatoes thinly. Heat oil in heavy large saucepan over medium heat. Add shallots and saute until tender, about 2 minutes. Add porcini and saute 1 minute. Add reserved porcini liquid, 2/3 cup cream, milk, salt and pepper and bring to simmer. Add potatoes, stirring gently to separate slices. Cook until potatoes begin to soften, stirring occasionally, about 15 minutes. Taste and adjust seasoning. Transfer to prepared dish. Spoon remaining 3 tablespoons cream over top of potatoes. (Can be prepared 1 day ahead. Refrigerate.) Bake until potatoes are tender, about 1 hour. Preheat broiler. Broil until top is browned, about 3 minutes.