01 - Preheat oven to 400°F (200°C). Position the rack in the center of the oven.
02 - Place each chicken breast between two sheets of parchment paper. Using a meat mallet, gently pound to an even 1/2 inch thickness throughout.
03 - Season the flour generously with salt and black pepper. Lightly dredge each flattened chicken breast in the seasoned flour, shaking off any excess coating.
04 - In a large oven-proof skillet, heat olive oil and butter over medium-high heat. Sear the dredged chicken breasts for 2 to 3 minutes per side until a golden crust forms. Remove and set aside on a plate.
05 - In the same skillet, sauté the finely chopped shallot until softened, about 2 minutes. Deglaze with the dry white wine and reduce by half. Stir in the crushed tomatoes and dried oregano, then simmer for 5 minutes. Season with salt and pepper to taste.
06 - Return the seared chicken to the skillet, nestling each breast into the sauce. Layer one slice of prosciutto followed by one slice of Fontina cheese atop each breast. Spoon a small amount of sauce over the topping.
07 - Transfer the skillet to the preheated oven. Bake for 10 to 12 minutes until the chicken is cooked through and the cheese is fully melted and bubbling.
08 - Remove from the oven and garnish with fresh basil leaves. Serve immediately while hot, accompanied by crusty bread or sautéed greens.