These Buttery Whole Onions That Melt in Your Mouth are the ultimate side dish. Roasted low and slow in garlic butter and fresh thyme, these onions become sweet, soft, and flavorful all the way through. Perfect with steak, chicken, or mashed potatoes, this onion recipe is comforting, elegant, and incredibly simple to make. Keywords: buttery onions, roasted onions, whole onion recipe, garlic butter onions, baked onion side dish.