Mashed Potato Gratin

Heat oven to 350 °F. Spray 13x9-inch (3-quart) glass baking dish with cooking spray. In 4-quart saucepan or Dutch oven, place potatoes; add enough water to cover potatoes by 1 inch. Heat to boiling over high heat. Reduce heat to medium-low; simmer uncovered 20 minutes or until potatoes are tender and can be easily pierced with fork. Drain potatoes; return to saucepan. Add butter; mash with potato masher until creamy. Stir in egg yolks, salt, milk and 1 cup of the cheese. Spread potato mixture evenly in baking dish. Sprinkle with remaining 1/2 cup cheese. Bake 30 minutes or until edges are light golden brown. Sprinkle with chopped parsley.