Gratin of Two Potatoes

Cook baking potatoes in large pot of boiling water 10 minutes . Add sweet potatoes; return to a boil. Simmer potatoes, uncovered, 25 minutes or until tender. Drain; cool under cold running water.

Meanwhile, melt butter in large nonstick skillet over medium-high heat. Add onion; cover and cook 3 minutes or until wilted. Uncover; cook over medium-low heat 10 to 12 minutes or until tender, stirring occasionally. Sprinkle with flour; cook 1 minute, stirring frequently. Add chicken broth, salt and pepper; bring to a boil over high heat. Reduce heat and simmer, uncovered, 2 minutes or until sauce thickens, stirring occasionally.

Preheat oven to 375°F. Spray 13X9-inch baking dish with nonstick cooking spray. Peel potatoes; cut crosswise into 1/4-inch slices. Layer half of baking and sweet potato slices in prepared dish. Spoon half of onion mixture evenly over potatoes. Repeat layers with remaining potatoes and onion mixture. Cover with foil. Bake 25 minutes or until heated through.

Preheat broiler. Uncover potatoes; sprinkle evenly with cheese. Broil, 5 inches from heat, 3 to 4 minutes or until cheese is bubbly and light golden brown.