Herbed Roast Chicken

Name: Herbed Roast Chicken
Ingredients: 1 whole chicken (about 5 pounds), trimmed of excess fat, giblets discarded (see note); 1/2 cup table salt for brining; 1/4 cup fresh tarragon leaves , lightly packed; 1 tablespoon fresh thyme leaves (see note); 6 medium scallions , green parts sliced thin (about 2/3 cup), whites reserved for another use; 1 medium garlic clove , minced or pressed through a garlic press (about 1 teaspoon); 1/4 teaspoon table salt; 1/4 teaspoon black pepper; 6 tablespoons unsalted butter , softened; 1 tablespoon vegetable oil; 1 - 1 1/2 cups low-sodium chicken broth; 2 teaspoons unbleached all-purpose flour; 1 teaspoon fresh lemon juice from 1 lemon