• 3 tablespoons (1/2 stick) butter
• 8 ounces mushrooms, sliced
• 4 –  5 cloves minced garlic
• 1 large onion, sliced about 3/8ths inch thick, pole to pole
• 1 teaspoon minced fresh thyme or abt 1/4 dried
• 3/4 cups chicken broth
• 1 cup whipping or heavy cream
• 1/8 cup dry white wine
• 1 teaspoon salt
• 1/4 teaspoon ground black pepper
• 1 1/2 to 2 pounds russet potatoes, peeled, thinly sliced into rounds (about 4 cups)
• 2 1/4 cups grated Gruyère or Swiss cheese (about 10 ounces)

Preheat oven to 400°F.  Butter 2 quart baking dish.

Melt butter in heavy large skillet over medium-high heat. Add mushrooms and and onions and gently sauté until with the lid on, about five to eight minutes, until the mixture is tender. Stir if needed. Remove the lid and continue to cook, stirring now and then, until the most of the liquid has evaporated and the mushrooms and onions are golden, a few minutes longer.

Add garlic and thyme and saute a minute or two longer and set aside. (May be made 1 day ahead. Cover and refrigerate.)

While the mushroom onion mixture is cooking, prepare your potatoes and set aside. In a large bowl, whisk broth, cream, wine, salt and pepper in large bowl to blend.

Layer the casserole:

Use 1/3 of the potatoes as the bottom layer, top with half the mushroom mixture and about 3/4 cup of cheese. Pour half the cream mixture over the top.

Add a second layer of potatoes, the rest of the mushroom mixture and another 3/4 cup of cheese. Top with the last layer of potatoes and pour the remaining cream mixture over the top. Reserve the remaining cheese.

Cover loosely (a piece of foil just layed over the top is ideal) and bake until potatoes are just tender and the sauce is bubbly, about an hour. Top with the remainder of the cheese and bake uncovered another 20 to 25 until the cheese is golden brown and the sauce has thickened. If necessary, the dish can be run under the broiler for a moment or two.

Let gratin stand 20 minutes before serving.

Notes:

• This is just a little tight in a standard 8 x 8 dish although the fancier 8 x 8 casseroles with the higher sides work. For maximum browning I like to use a shallow, oval au gratin pan.
• Depending on the pan I use, I might place a sheet of foil on a tray on the next rack below the potatoes to catch any drips.

from the kitchen of http://www.frugalhausfrau.com