Cook first 3 ingredients in butter in a Dutch oven over medium heat, stirring constantly, until tender. Add whipping cream and next 3 ingredients; bring to a boil, stirring occasionally. Stir in potato.
Spoon mixture into a lightly greased 2 1/2-quart shallow baking dish; sprinkle with cheeses.
Bake at 350° for 1 hour or until potato is tender. (Cover with aluminum foil the last 10 minutes of baking, if necessary, to prevent excessive browning.) Let stand, covered, 10 minutes.