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 with salt and pepper on a shallow plate. Lightly 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 dredged chicken 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 for about 2 minutes until softened. Deglaze with white wine and let it reduce by half. Stir in the crushed tomatoes and dried oregano, then simmer for 5 minutes. Adjust salt and pepper to taste.
06 - Return the chicken breasts to the skillet, nestling them into the sauce. Lay one slice of prosciutto over each breast, followed by one slice of Fontina cheese. Spoon a little sauce over the top.
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 bubbly.
08 - Remove from the oven, garnish with fresh basil leaves, and serve hot with crusty bread or sautéed greens alongside.