4 tablespoons unsalted butter, 2 lbs peeled and trimmed onions, Salt and pepper

1. Adjust oven rack to center position and preheat oven to 325°. 2. Melt butter in a large non-stick or cast iron skillet over medium heat. Add onions and toss to coat. 3. Season to taste with salt and pepper. If using a non-stick pan, transfer to a baking sheet. 4. Transfer to oven and roast, tossing occasionally, until deeply caramelized and tender, about 30 minutes. 5. Serve immediately.