For the Potatoes and Caramelized Onions:
Preheat the oven to 425 degrees. Cut ⅛ -¼ inch slices crosswise down the length of each potato, not cutting all the way through so that the potato remains together at the bottom. Place in a 9x13 baking dish, cut side up. Combine olive oil and melted butter together in a small bowl.
Scatter onion slices around the potatoes. Brush the onions and potatoes with the olive oil and butter mixture and season with salt and pepper. Transfer to the oven and bake for 30 minutes.
Remove the baking dish from the oven. Stir the onions and brush the potatoes again with the oil and butter mixture. Return to the oven and bake for 20 to 30 minutes more or until the potatoes are tender.
Meanwhile, make the Sage Butter: Combine butter and sage in a small bowl and season to taste with salt. Set aside.
Remove the baking dish from the oven and increase the oven temperature to 450 degrees. Gather the onions from the bottom of the dish with a spoon or fork and scatter them evenly over the top of the potatoes. Dot potatoes with Sage Butter. Return to the oven and bake for an additional 5 minutes. Serve.
Calories: 253kcal | Carbohydrates: 39g | Protein: 5g | Fat: 9g | Saturated Fat: 4g | Cholesterol: 15mg | Sodium: 14mg | Potassium: 923mg | Fiber: 5g | Sugar: 2g | Vitamin A: 175IU | Vitamin C: 43mg | Calcium: 39mg | Iron: 2mg