Scalloped Potato Duo with Ham

From : "Christmas with Southern Living 2003"

1 medium onion, coarsely chopped
1 tablespoon vegetable oil
3 garlic cloves, finely chopped
2 sweet potatoes, peeled and cut into quarter inch slices (about 1.5 pounds)
2 baking potatoes, peeled and cut into quarter inch slices (about 1.5 pounds)
1/2 cup all-purpose flour
1 teaspoon salt
1/4 teaspoon pepper
2 cups chopped ham
2 cups (8 ounces) shredded Gruyere cheese, divided
1 3/4 cup whipping cream
2 tablespoons butter, cut into pieces

Saute onion in oil over medium-high heat 5 minutes. Add garlic; cook 30 seconds. Remove from heat and set aside. Place potatoes in a large bowl.
Combine flour salt, and pepper; sprinkle over potatoes, tossing to coat. Arrange half of potato mixture in a greased 13" x 9" baking dish or 3-quart gratin dish. Top with onion, ham and 1 cup cheese. Top with remaining potato mixture. Pour cream over potato mixture. Dot with butter, and cover with aluminum foil.
Bake at 400 degrees F for 50 minutes. Uncover top with remaining 1 cup cheese and bake 20 more minutes or until potatoes are tender and chees is browned. Let stand 10 minutes before serving. Yield 6 to 8 servings.