PREHEAT oven to 350°F. Lightly spray large skillet with cooking spray; heat on medium-high heat.

ADD onion; cook 5 to 7 min. or until tender, stirring often. Add cream cheese, broth and mustard; mix well. Remove from heat; set aside.

LIGHTLY spray 13x9-inch baking dish with cooking spray. Toss potatoes with cream cheese mixture; spoon into prepared pan. Combine crushed crackers, Parmesan cheese, butter and parsley; sprinkle evenly over potatoes.

BAKE 50 min. to 1 hour or until potatoes are tender. Let stand 5 min. before serving.