Preheat the oven to 350 degrees F. Put potatoes, yams, milk, salt, and pepper into a saucepan over medium heat, bring to a simmer and cook until potatoes and yams are partially cooked?about 10 minutes. Pour out the potatoes and milk into a buttered and salt and pepper-seasoned 9 by 13-inch baking pan. Arrange potatoes so they are evenly layered. Sprinkle top with cheese and chives.
Cover pan with foil and bake until potatoes are tender, about 35 to 45 minutes. Remove the foil and raise the temperature to 400 degrees F. Continue to bake another 15 minutes and then broil until the top is golden brown.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.