Sweet and Savory Baked Chicken with Pineapple and Tarragon

INGREDIENTS

• 4 sprigs fresh tarragon (2 sprigs chopped, 2 whole sprigs for roasting), plus more for garnish
• Coarse salt and freshly ground pepper
• 1 whole chicken (about 4 1/2 pounds), cut into pieces
• 2 cups chopped fresh pineapple
• 8 shallots (2 coarsely chopped, 6 halved lengthwise)
• 2 tablespoons rice-wine vinegar
• 1/2 teaspoon sugar
• 1 tablespoon unsalted butter