- 1 1/2 cups crème fraîche
- 1/3 cup whipping cream
- 3 pounds Yukon Gold potatoes, peeled, cut into 1/8-inch-thick slices
- 1 1/2 teaspoons coarse kosher salt
- 3/4 teaspoon ground black pepper
- 1 1/2 teaspoons dried thyme
- Place rack in center of oven and preheat to 400°F. Generously butter 13x9x2-inch glass or ceramic baking dish. Whisk crème fraîche and whipping cream in medium bowl to blend.
- Arrange 1/3 of potato slices in bottom of prepared baking dish, overlapping slightly. Sprinkle with 1/2 teaspoon salt, 1/4 teaspoon pepper, and 1/2 teaspoon thyme. Drop 1/3 of crème fraîche mixture (about generous 1/2 cup) in dollops over potatoes, then spread evenly over (layer will be very thin). Repeat layering 2 more times.
- Bake gratin 30 minutes. Reduce oven temperature to 350°F and continue to bake until potatoes are tender and top is golden brown, about 25 minutes longer. Let gratin rest 20 minutes before serving. DO AHEAD Can be made 2 hours ahead. Cover loosely with foil. Let stand at room temperature. Before serving, rewarm in 350°F oven until heated through, about 15 minutes.