• From The Art of Simple Food II by Alice Waters
• Yields 4 servings

Yellow Finn potatoes are rich in flavor and have the perfect texture for a gratin. They become soft and luscious without breaking down into a puree. For added color, alternate with rows of red-fleshed potato such as Cranberry Red. Black trumpet mushrooms (also called black chanterelles or horn-of-plenty mushrooms) can harbor sand. Be sure to rinse them well before cooking.

Gently tear in half lengthwise:

¼ pound black trumpet mushrooms

Swish them in a bowl of cool water to clean; drain well. Heat a heavy-bottomed pan over medium heat. Measure in:

1 teaspoon butter or oil

Add:

A pinch of salt

1 large thyme sprig

Fresh-ground black pepper

When the butter has melted, add the mushrooms and cook, stirring now and then, until all the water has evaporated and the mushrooms just start to sizzle. Remove from the heat to cool. Taste for salt and add more as needed. Remove the thyme sprig.

Peel:

2 pounds potatoes (Yellow Finn, Cranberry Red or Yukon Gold)

Hold in cool water until ready to use to keep them from browning.

Rub a 6-inch-by-8-inch baking dish with:

A peeled garlic clove

Allow to dry a little and rub the dish with

2 teaspoons butter

Measure:

2/3 cup crème fraiche

Pour into a small pot and warm:

½ cup half-and-half

A pinch of salt

Once all the ingredients are prepared, preheat the oven to 375 F. Slice the potatoes ¼-inch thick. Use a mandoline slicer or a sharp knife to make the slices as consistent as possible. Using one-third of the sliced potatoes, make a layer of potato slices on the bottom of the baking dish. Season with:

Salt

Fresh-ground black pepper

Spoon one-third of the crème fraiche over the potatoes, followed by half the mushrooms. Repeat, making another layer with half the remaining potato slices. Add seasoning, half the remaining crème fraiche and the rest of the mushrooms.

For the last layer of potatoes, carefully arrange rows of potato slices overlapped like shingles and completely covering the surface.

Dot the surface with the last of the crème fraiche and gently add the half-and-half, pouring down the sides of the baking dish to avoid washing off the crème fraiche and salt.

Put the gratin in the oven and bake until tender and golden, about 1 hour. After it has been cooking for 35 minutes, press the top layer of potatoes under the cream with a spatula. Press again after another 15 minutes. This keeps them from drying out.

When done, the potatoes should be very soft, the top golden and the liquid mostly gone. If the potatoes begin to brown too much before being cooked through, loosely cover the top with a bit of foil.