COMBINE dressing, milk and cheese in a microwaveable bowl. Microwave on HIGH power for 2 to 3 minutes, stirring once during cooking.
PLACE 1/2 cup (125 mL) sauce on the bottom of a lightly greased 9 x13 inch (33 x 23 cm) baking dish. Layer with potatoes, ham and onion. Pour remaining sauce over top.
COVER and bake at 350°F (180°C) for 20 minutes.
REMOVE cover and bake 10 minutes longer or until lightly browned.
