3 pounds russet potatoes, peeled, cut into 1/8-inch-thick rounds
1 1/2 cups crème fraîche, (stirred to loosen)
2 tablespoons chopped fresh thyme
1 1/2 cups (packed) grated Gruyère cheese (about 6 ounces)
2 tablespoons chopped fresh Italian parsley

Preheat oven to 400°F. Generously butter 13x9x2-inch glass baking dish. Arrange half of potato slices in bottom of prepared dish, overlapping slightly. Sprinkle generously with salt and pepper. Spread half of crème fraîche over potatoes and sprinkle with half thyme and half of cheese .

Top with remaining potatoes, overlapping slightly; sprinkle generously with salt and pepper. Spread with remaining crème fraîche; sprinkle with remaining thyme and cheese.
Bake gratin uncovered 30 minutes. Reduce oven temperature to 350°F. Continue to bake gratin until potatoes are tender and top is golden brown, about 45 minutes. Remove from oven; let stand 10 minutes. Sprinkle with parsley and serve.

Makes 8 servings.