1/2 lb fresh wild or exotic mushrooms such as chanterelles or shiitakes (discard the shiitake stems if you use those), trimmer and coarsely chopped. You can mix any kind of mushrooms you find at the market.
2 1/2 tablespoons unsalted butter
3/4 lb fresh cremini mushrooms, trimmed and sliced 1/4 inch thick
1 1/2 teaspoons minced garlic
3 lb russet (baking) potatoes
1 1/2 cups heavy cream
1 1/2 cups whole milk
1 1/2 teaspoons salt
1/2 teaspoon white pepper
1/4 teaspoon freshly grated nutmeg
2 oz grated Gruyere cheese (about 1 cup)
Place the rack in the middle of the oven and preheat to 400 (F).
Cook chanterelles or shiitakes with salt and pepper to taste in one (1) tablespoon butter in a large nonstick skillet over moderate heat, stirring, until liquid mushrooms give off its evaporated and mushrooms are tender, about eight (8) minutes. Transfer to a bowl.
Cook cremini in remaining 1 1/2 tablespoons butter in skillet, stirring, until liquid is evaporated and mushrooms are tender, about eight (8) minutes, then transfer to the bowl with the wild mushrooms. Toss the mushrooms with 1 teaspoon garlic.
Peel potatoes and cut crosswise into 1/8 inch thick slices.
Bring potatoes, cream, milk, salt, white pepper, nutmeg and remaining 1/2 teaspoon garlic to a boil in a 4-6 quart heavy pot, stirring once or twice, then remove from heat.
Transfer half of the potatoes to a buttered gratin dish with a slotted spoon, spreading evenly.
Spread mushroom s evenly over potatoes, then top with the remaining potatoes.
Pour the cooking liquid over the potatoes and sprinkle with cheese.
Bake gratin until the top is golden brown and potatoes are tender, about 45-55 minutes. Let stand ten (10) minutes before serving.
Serves eight (8) persons.
I first served this dish with veal, and then with chicken, then with steak. It goes well with any full-taste dish.