Ingredients

• 6 (about 2 1/2 pounds total) bone-in, skin-on chicken thighs

• 2 tablespoons, plus 2 teaspoons olive oil, divided

• 2 teaspoons kosher salt, divided

• 1 teaspoon black pepper, divided

• 1 frozen puff pastry sheet, thawed (from 1 [17.3-ounce] package)

• 1 large egg, beaten

• 2 tablespoons unsalted butter

• 2 medium-size (about 1 pound, 4 ounces total) yellow onions, halved lengthwise and sliced 1/4-inch-thick (4 1/2 cups)

• 2 large (6 ounces total) carrots, peeled and cut into 1/2-inch cubes (1 cup)

• ¼ cup water

• 1 tablespoon minced garlic (from 3 garlic cloves)

• ¼ cup dry sherry

• 3 tablespoons all-purpose flour, plus more for work surface

• 2 cups beef stock

• 2 teaspoons chopped fresh thyme, plus more for garnish

• ¾ teaspoon chopped fresh rosemary

• 4 ounces shredded Gruyère cheese, shredded (1 cup)