Butter the sides and bottom of a 30 x 20-cm (12 x 8-inch) baking dish. Line the bottom of the dish with slices of sweet potatoes. Sprinkle with cheese and drizzle with cream. Season with salt and pepper. Cover with a layer of potatoes, drizzle with cream and sprinkle with chives. Continue with all the ingredients and season with salt and pepper between each layer. Cover with aluminum foil.