A ham filling sandwiched between layers of potatoes turns this gratin into a main-dish casserole.
Heat oven to 350°F. Lightly oil 13 x 9 x 2-inch glass baking dish.
Bring large pot of lightly salted water to boiling over high heat. Add potato; partially cover; cook 2 minutes. Drain and reserve.
Mix ham, egg, butter, salt, pepper and cloves in processor. Pulse to combine. Add chicken, milk and half-and-half. Process until smooth.
Arrange half the potatoes to cover bottom of prepared dish. Evenly spread ham mixture over potatoes. Arrange remaining potatoes over top.
Melt butter in saucepan over medium heat. Stir in flour; cook, stirring, 1 minute. Whisk in 1 cup milk; cook until smooth and just beginning to thicken, 2 to 3 minutes. Stir in remaining cup milk, the salt, pepper and nutmeg. Cook, stirring occasionally, until thickened and bubbly, 4 to 5 minutes.
Pour white sauce into baking dish. Sprinkle Parmesan over top.
Bake in 350°F oven 45 minutes, until browned. Let stand 15 minutes. Garnish with chopped parsley.