Cook bacon in a large ovenproof skillet over medium-high heat for 6 to 7 minutes or until crisp, turning occasionally. Drain on paper towel-lined plate; crumble into medium bowl. Drain all but 1 Tablespoon of drippings from skillet.
Add onions to skillet; cook and stir over medium heat about 8 minutes or until translucent but not browned. Drain on paper towel-lined plate. Transfer to bowl with bacon; mix well.
Reserve 1/4 cup cheese; set aside. Melt 1 Tablespoon butter in same skillet or 8" to 9" baking dish. Arrange one quarter of potato slices to cover bottom of skillet. Season with salt and pepper. Top with one third of bacon-onion mixture; sprinkle with one third of remaining cheese. Repeat layers twice. Top with remaining one quarter of potato slices; dot with remaining 1 Tablespoon butter.
Cover with foil and bake 50 minutes. Uncover and bake 10 minutes or until potatoes are tender. Turn oven to "broil"; broil 2 to 3 minutes or until lightly browned. Sprinkle with reserved 1/4 cup cheese. Serve warm.
**Tip: Use a mandolin to slice the potatoes very thin (about 1/8"). Thicker pieces will require longer cooking time.