1Season the chicken breasts with salt and pepper. Lie the breasts boned side up on a work surface. Top with the prosciutto and Fontina, folding it to fit evenly on each chicken breast half and leaving a border around the entire breast. Roll the breasts lengthwise to enclose the filling and tie tightly with kitchen string in 4 to 5 places to secure the chicken.
2Preheat the oven to 400°F. In a large, heavy, ovenproof frying pan, warm the olive oil and 2 tablespoons of butter over medium-high heat. Add the rolled chicken breasts and pan-sear, turning often, until browned all over, about 8 minutes. Drain off all but about 2 tablespoons of the fat. Transfer to the oven to finish cooking, about 10 minutes; the chicken should read 165°F at the center when tested with a meat thermometer. Set aside to rest for about 10 minutes while you make the sauce.
3In a frying pan, melt 2 tablespoons of the butter. Sauté the shallot, mushrooms, thyme, and a pinch of salt, stirring, until the mushrooms are tender, about 5 minutes. Stir in the chicken broth and white wine and simmer until the sauce thickens slightly, about 10 minutes. Stir in the remaining 1 tablespoon of butter. Remove the thyme stems. Serve the chicken with the sauce.
Baking boneless, skinless chicken breasts often results in a bland, dried-out dinner. But with a few quick tricks and our simple Crispy Baked Chicken Breasts recipe, the CHOW Test Kitchen's Amy Wisniewski shows you how to get juicy, flavorful meat every time.