Chicken Stuffed with Golden Onions & Fontina

Ingredients
4 teaspoons extra-virgin olive oil , divided
1 1/2 cups thinly sliced red onion
2 teaspoons minced fresh rosemary , divided
1/8 teaspoon salt
Freshly ground pepper to taste
2/3 cup shredded fontina cheese , preferably aged
(I think I will use mozzarella cheese)4 boneless, skinless chicken breasts (about 1 pound), trimmed of fat
1/2 cup white wine
1 cup reduced-sodium chicken broth
4 teaspoons all-purpose flour


Recipe Directions
Heat 2 teaspoons oil in a large nonstick skillet over medium-high heat. Add onion and 1 teaspoon rosemary; cook, stirring occasionally, until the onion is golden brown, 6 to 7 minutes. Season with salt and pepper. Let cool; stir in fontina.
Meanwhile, cut a horizontal slit along the thin, long edge of each chicken breast half, nearly through to the opposite side. Stuff each breast with 1/4 cup of the onion-cheese mixture.
Heat the remaining 2 teaspoons oil in the same skillet over medium-high heat. Add the chicken and cook until golden, about 5 minutes per side. Transfer to a plate and cover with foil to keep warm.
Add wine and the remaining 1 teaspoon rosemary to the pan. Cook over medium-high heat for 2 minutes. Whisk broth and flour in a bowl until smooth; add to the pan, reduce heat to low and whisk until the sauce thickens, about 1 minute. Return the chicken to the pan and coat with the sauce. Cook, covered, until the chicken is just cooked through, 2 to 4 minutes. Serve the chicken topped with the sauce.