Preheat oven to 400F. 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 creme fraiche over potatoes and sprinkle with half of cheese. Top with remaining potatoes, overlapping slightly; sprinkle generously with salt and pepper. Spread with remaining creme fraiche; sprinkle with remaining cheese. Bake gratin uncovered 30 minutes. Reduce oven temperature to 350F. Continue to bake gratin until potatoes are tender and top is golden brown, about 45 minutes. Sprinkle with parsley and serve.