Ingredients
1 small chicken (about 3 1/2 pounds), room temperature, halved and patted dry
Kosher salt and freshly ground pepper
2 tablespoons unsalted butter
2 tablespoons extra-virgin olive oil
1 1/2 pounds mixed Italian frying peppers, sliced (about 7 cups total)
1 small onion, sliced (1 1/2 cups)
3 cloves garlic, thinly sliced
1/2 cup low-sodium chicken broth
1/2 cup red-wine vinegar
2 tablespoons sugar
3 tablespoons capers, drained
2 sprigs rosemary (each about 4 inches)
Creamy polenta for serving
Preparation
Preheat oven to 450°F with a rack in center. Season all sides of chicken generously with salt and pepper. Heat a large nonstick skillet over medium; add butter and 1 tablespoon oil.
When butter melts and foam subsides, add chicken, skin-side down. Place a piece of foil on top of chicken and top with a second heavy skillet to weigh down. Cook, undisturbed, until skin forms a golden-brown crust, 10 to 12 minutes. Remove top skillet and foil. Transfer chicken to a plate, skin-side up.
Discard fat in skillet. Return to medium-high heat and add remaining 1 tablespoon oil. Add peppers and onion, season with salt, and cook, stirring occasionally, until vegetables are browned in places, 4 to 5 minutes. Add garlic and cook, stirring, until fragrant, about 30 seconds. Stir in broth, vinegar, sugar, capers, and rosemary; season with salt and pepper. Bring mixture to a boil, then transfer to a 9-by-13-inch roasting pan or baking dish along with chicken, skin-side up, and any accumulated juices.
Roast until a thermometer inserted into thickest part of chicken reads 160°, about 20 minutes. Transfer chicken to a plate and loosely tent with foil. Return vegetables to oven; cook until sauce has reduced slightly, about 10 minutes more. Season. Serve chicken with vegetables and polenta, spooning juices over top.
