Golden Potato Gratin with Wild Mushrooms

1 tbsp unsalted butter for greasing the baking dish
2 oz dried mushrooms such as porcini or a combination of porcini and chanterelles
2 cups crème fraiche
1/2 cup half-and-half
3 1/2 pounds Yukon Gold potatoes, peeled and cut into 1/8-inch thick rounds
Kosher salt
Freshly ground black pepper
2 tsp dried thyme leaves
1 1/2 tsp dried crushed rosemary
3/4 cup (3 to 4 oz) grated white cheddar
3 to 4 tbsp toasted breadcrumbs (Recipe follows.)
Fresh rosemary and thyme sprigs for garnish, optional

1. Arrange a rack at center position and preheat oven to 400 degrees F. Butter a 3 1/2- to 4-quart oven-to-table baking dish (a 9x13-inch dish works well).

2. Place the dried mushrooms in a medium bowl and cover with 1 1/2 cups boiling water. Let stand until softened, about 20 minutes. Strain the mushrooms over a bowl in a fine mesh sieve lined with paper towels, pressing down on them with a wooden spoon to release as much liquid as possible. Chop mushrooms into large pieces and set them aside. (Save the drained liquid for another use: you can add it to gravy or use it to deglaze a pan in which meat or poultry has been sautéed.)

3. In a medium bowl whisk together the crème fraîche and half-and-half.

4. Arrange one fourth of the potato slices in the bottom of the baking pan, overlapping them slightly. Season them generously with salt and pepper and with 1/2 teaspoon of the thyme. Sprinkle one third of the mushrooms over the layer and season them very lightly with salt and pepper and 1/2 teaspoon of the rosemary. Spread one-fourth of the crème fraiche mixture over the potatoes. Repeat to make 2 more layers. Make a final layer of potatoes, season them with salt, pepper, and remaining 1/2 teaspoon thyme. Cover with a final layer of the crème fraîche mixture. Sprinkle with cheese, and cover the pan tightly with foil.

5. Bake the gratin 30 minutes, then reduce heat to 350 degrees F and remove the foil. Continue to cook until the potatoes are tender when pierced with a sharp knife and top is golden brown, 30 to 40 minutes more.

6. Remove gratin from the oven and sprinkle 3 to 4 tablespoons of the toasted bread crumbs over the top. Let gratin stand 20 minutes before serving. If desired, garnish the gratin with a few rosemary and thyme sprigs. (The gratin is best when made and served within 20 minutes. However you can cook it up to 4 hours ahead and reheat it. Cool the gratin, cover loosely with foil, and leave at room temperature. Reheat, uncovered, in a preheated 350 degree F oven until hot, about 20 minutes.)

Serves 8

Toasted Bread Crumbs

Half of a good-quality peasant or country bread (sourdough works particularly well) with crusts removed
1 tbsp olive or canola oil

1. In a food processor, process enough slices to make 1 cup coarse crumbs.

2. Heat the oil in a medium, heavy frying pan over medium heat. When hot, add crumbs and cook, stirring constantly, until crisp and rich golden brown, 3 to 4 minutes. (Store the bread crumbs in a plastic self-sealing bag and refrigerate for up to one week.)

Copyright Betty Rosbottom 2016