Cut potatoes into 1/8-inch-thick slices; set aside.
Melt butter in a Dutch oven over medium-high heat; add green onions and next 3 ingredients. Cook, stirring constantly, 2 minutes. Add whipping cream and next 3 ingredients, stirring well.
Add potato slices; bring to a boil over medium heat, and cook, stirring gently, 15 minutes or until potato slices are tender. Spoon into a lightly greased 11- x 7- x 1 1/2-inch baking dish; sprinkle with cheeses.
Bake at 350° for 45 minutes or until bubbly and golden brown. Let stand 15 minutes before serving.