In a large skillet heat 3 tablespoons clarified butter over moderate heat and saute the shallots until golden. Add the sliced mushrooms and cook, stirring frequently, until mushrooms release their liquid and the liquid has evaporated. Season the mushrooms with the nutmeg, salt and pepper. Remove the skillet from the heat and set aside.
Peel a potato and coarsely grate into a bowl of cold water. Repeat procedure for the remaining potatoes. Heat 3 tablespoons clarified butter in a 6- to 8-inch heavy skillet over moderate heat until hot but not smoking. Drain 1/2 of the grated potatoes on paper towels and pat dry. Season with salt and pepper and toss to combine. In the heated skillet carefully spread out half of the seasoned potatoes. Top with half of the cooked mushrooms and then spread the other half of the seasoned potatoes on top. Using a spatula gently press down the potatoes and drizzle with 1 to 2 tablespoons of clarified butter. Cook until golden brown about 15 minutes.
When potato cake is golden brown gently slide it on to a flat pot lid or plate. Invert skillet over potato cake and flip, uncooked side down, into skillet. Drizzle 3 tablespoons butter around edges of the potato cake and continue to cook until golden brown. Transfer to a baking sheet and keep warm in 300 degree F. oven. Repeat process with remaining potatoes and mushrooms. Cut potato and mushroom cakes into wedges and serve hot.
Recipe courtesy of Gourmet Magazine