Potato-Mushroom Gratin

Ingredients

• 1.5 teaspoons coarse kosher salt plus additional for mushrooms
• 12 ounces crimini mushrooms fresh sliced (baby bella)
• 2 tablespoons thyme leaves fresh chopped
• 6  garlic cloves thinly sliced
• 1.3 cups heavy whipping cream divided ()
• 5 tablespoons olive oil divided
• 3 ounces parmesan cheese divided freshly grated
• 0.8 teaspoon pepper plus additional black freshly ground for mushrooms
• 2.5 pounds yukon gold potatoes peeled cut lengthwise into 1/8-inch-thick slices

Equipment

• baking sheet
• oven
• baking pan
• aluminum foil

Directions

1. Preheat oven to 375°F.
2. Brush 13x9x2-inchglass or oval ceramic baking dish with2 tablespoons oil. Arrange 1/3 of potatoes,slightly overlapping, in dish.
3. Sprinkle with1/2 teaspoon coarse salt and 1/4 teaspoonpepper.
4. Pour 1/3 cup cream over; sprinklewith 1/4 cup cheese. Repeat layering 1/3 ofpotatoes, 1/2 teaspoon salt, 1/4 teaspoonpepper, 1/3 cup cream, and 1/4 cup cheese 2more times.
5. Bake uncovered until potatoesare tender, adding cream by tablespoonfulsif dry, about 45 minutes.
6. Remove from oven;maintain oven temperature.
7. Sprinkle thyme and garlic slices overgratin. Toss mushrooms in medium bowlwith 3 tablespoons oil; sprinkle with coarsesalt and pepper. Arrange mushroom slicesatop gratin around edge of dish.
8. Drizzlewith 1/4 cup cream; sprinkle with 1/4 cupcheese. Continue to bake uncovered untilmushrooms are tender and potato edgesare golden brown, about 20 minutes longer.DO AHEAD: Can be made 1 day ahead.Cool 1 hour in dish; cover and chill. Beforeserving, cut gratin into 10 pieces.
9. Transferto rimmed baking sheet. Cover with foil andrewarm in 350°F oven, 10 to 15 minutes.