1. In a large saucepan cook potatoes, covered, in boiling lightly salted water about 5 minutes or until slightly tender but still firm. Drain; set aside. In a large skillet heat olive oil over medium-high heat. Add pancetta; cook until lightly browned. Using a slotted spoon, remove pancetta, reserving drippings in skillet. Set pancetta aside. Add onions to skillet. Cook and stir over medium-low heat about 20 minutes or until lightly browned and very tender. Remove from heat. Carefully stir potatoes and pancetta into onions in skillet.

2. Lightly butter a 2-quart rectangular baking dish. Spread potato mixture into prepared dish. In a medium bowl whisk together eggs and milk. Add cheese, salt, rosemary, and pepper; stir until well mixed. Pour evenly over potato mixture in baking dish.

3. Preheat oven to 350°F. Bake, uncovered, for 45 to 50 minutes or until golden and a knife inserted in the center comes out clean. Let stand for 15 minutes before serving.

Make-Ahead Tip

Prepare as directed. Cover; chill for at least 4 hours or up to 24 hours. Preheat oven to 350°F. Bake, uncovered, for 45 to 50 minutes or until golden and a knife inserted in the center comes out clean. Let stand for 15 minutes before serving.