01 - Preheat oven to 400°F (200°C). Position the rack in the center.
02 - Place each chicken breast between two sheets of parchment paper. Using a meat mallet, gently pound to an even 3/8-inch thickness.
03 - Season the flour generously with salt and black pepper in a shallow dish. Dredge each flattened chicken breast in the seasoned flour, shaking off any excess.
04 - Heat olive oil and butter in a large oven-proof skillet over medium-high heat. Sear the chicken for 2–3 minutes per side until a golden crust forms. Remove the chicken and set aside on a plate.
05 - In the same skillet, sauté the finely chopped shallot for about 2 minutes until softened. Deglaze with the dry white wine, scraping up any browned bits, and let it reduce by half. Stir in the crushed tomatoes and dried oregano. Simmer for 5 minutes, then adjust seasoning with salt and pepper as needed.
06 - Return the seared chicken breasts to the skillet, nesting them into the sauce. Lay one slice of prosciutto over each breast, followed by a slice of Fontina cheese. Spoon a small amount of sauce over the top of each piece.
07 - Transfer the skillet to the preheated oven. Bake for 10–12 minutes until the chicken is cooked through (internal temperature reaches 165°F) and the cheese is fully melted and bubbling.
08 - Remove from the oven and garnish with fresh basil leaves. Serve immediately, accompanied by crusty bread or sautéed greens.