Preheat oven to 400°. Quarter onion (do not peel) and combine with 1 tablespoon oil and salt to taste in a small mixing bowl. Toss well to combine. Place on a baking sheet and roast until very brown, about 20 minutes. Remove from oven and allow to cool. Peel away outer, dried layers of onion and discard. Cut wedges into 1-inch pieces.

. Heat remaining 2 tablespoons oil in a large sauté pan over high heat. Once sizzling, add kale. Sauté, stirring often, until leaves turn a bright green. Add onions, balsamic, raisins, and red pepper flakes. Season with salt, and stir well. Transfer to a serving bowl and serve immediately.