Preheat oven to 400°.
Butter 9x13-inch baking dish with 2-inch sides.
Stir whipping cream and Boursin cheese in heavy large saucepan over medium heat until cheese melts and mixture is smooth.
Arrange half of sliced potatoes in baking dish in slightly overlapping rows.
Generously season potatoes with salt and pepper.
Pour half of cheese mixture over.
Arrange remaining potatoes as before.
Generously season with salt and pepper.
Pour remaining cheese mixture over potatoes.
Bake until top is golden brown and potatoes are tender when pierced with knife - about 1 hour.
Sprinkle with chopped fresh parsley and serve.