Potato Mushroom Gratin

Layers of thinly sliced potatoes are layered with cream, parmesan cheese and salt and pepper. Once they've baked up bubbly and golden you then top them off with slices of garlic, fresh thyme and baby portabella mushrooms. This wonderful concoction get another trip to the oven and you end up with a rich and creamy potato, mushroom gratin. Delicious.

Potato Mushroom Gratin

Ingredients
5 tablespoons olive oil, divided
2 1/2 pounds medium Yukon Gold potatoes, peeled, cut lengthwise into 1/8-inch-thick slices
1 1/2 teaspoons coarse kosher salt plus additional for mushrooms
3/4 teaspoon freshly ground black pepper plus additional for mushrooms
1 1/4 cups (or more) heavy whipping cream, divided
1 cup freshly grated Parmesan cheese (about 3 ounces), divided
2 tablespoons chopped fresh thyme
6 garlic cloves, thinly sliced
12 oz fresh crimini (baby bella) mushrooms, sliced

Preparation
Preheat oven to 375°F. Brush 13x9x2-inch glass or oval ceramic baking dish with 2 tablespoons oil. Arrange 1/3 of potatoes, slightly overlapping, in dish. Sprinkle with 1/2 teaspoon coarse salt and 1/4 teaspoon pepper. Pour 1/3 cup cream over; sprinkle with 1/4 cup cheese. Repeat layering 1/3 of potatoes, 1/2 teaspoon salt, 1/4 teaspoon pepper, 1/3 cup cream, and 1/4 cup cheese 2 more times. Bake uncovered until potatoes are tender, adding cream by tablespoonfuls if dry, about 45 minutes. Remove from oven; maintain oven temperature.

Sprinkle thyme and garlic slices over gratin. Toss mushrooms in medium bowl with 3 tablespoons oil; sprinkle with coarse salt and pepper. Arrange mushroom slices atop gratin around edge of dish. Drizzle with 1/4 cup cream; sprinkle with 1/4 cup cheese. Continue to bake uncovered until mushrooms are tender and potato edges are golden brown, about 20 minutes longer.

DO AHEAD Can be made 1 day ahead. Cool 1 hour in dish; cover and chill. Before serving, cut gratin into 10 pieces. Transfer to rimmed baking sheet. Cover with foil and rewarm in 350°F oven, 10 to 15 minutes.