Ingredients

• 2 tablespoons extra-virgin olive oil

• 3 pounds bone-in, skin-on chicken thighs (about 8 small thighs), trimmed

• 1 teaspoon black pepper

• 2 1/2 teaspoons kosher salt, divided, plus more to taste

• 4 medium carrots (about 1 pound), peeled and chopped

• 1 yellow onion, chopped

• 5 garlic cloves, finely chopped

• 3/4 cup apple cider vinegar

• 2 tablespoons whole-grain mustard

• 3 cups chicken broth

• 1 tablespoon cornstarch

• 1 tablespoon water

• 5 tablespoons unsalted butter, cubed and chilled

• 2 tablespoons chopped fresh tarragon

• 2 tablespoons thinly sliced fresh chives, divided