Ingredients

1 pound small cipollini (about 22), root ends trimmed

8 ounces pearl onions (mix of white and red; about 30), root ends trimmed

8 ounces small shallots (about 6), root ends trimmed, peeled

3/4 cup dry red wine

3/4 cup red-wine vinegar

1/4 cup balsamic vinegar

3 tablespoons honey

2 1/2 teaspoons coarse salt

2 tablespoons extra-virgin olive oil

1 fresh bay leaf

1 large sprig fresh rosemary, plus more for garnish

Freshly ground pepper

4 boneless, skinless chicken breast halves (about 6 ounces each)

Vegetable-oil cooking spray

Preparation

Bring 2 inches of water to a simmer in a large stockpot. Set a steamer insert in pot, and add cipollini, pearl onions, and shallots. Cover, and steam until tender, 10 to 12 minutes. Transfer to a plate, and let cool slightly, about 10 minutes. Peel cipollini and pearl onions, leaving tops and root ends intact; set aside.

Stir wine, vinegars, honey, and 2 teaspoons salt in a small bowl; set aside.

Heat 1 tablespoon oil in a large skillet over medium heat. Add cipollini, pearl onions, shallots, bay leaf, and rosemary sprig. Cook, stirring often, until cipollini, onions, and shallots are deep golden brown in spots, about 5 minutes.

Add vinegar mixture to skillet. Reduce heat to medium-low, and simmer, stirring occasionally, until liquid is syrupy, about 30 minutes. Discard rosemary and bay leaf. Season with pepper.

Meanwhile, preheat broiler, with rack 6 inches below heat source. Butterfly chicken: Using a chef’s knife and starting on one long side, slice chicken open horizontally, stopping about 1/2 inch before reaching opposite side. Open each piece of chicken like a book, and place it between two pieces of plastic wrap. Pound chicken to 1/4 inch thick.

Coat a rimmed baking sheet with cooking spray. Brush chicken on both sides with remaining tablespoon oil, and season with remaining 1/2 teaspoon salt and 1/4 teaspoon pepper. Transfer to the prepared sheet; broil chicken, flipping once, until golden brown and cooked through, about 3 1/2 minutes per side.

Transfer chicken to a serving platter, and add cipollini, pearl onions, and shallots. Garnish with rosemary sprigs.