01 - Preheat your oven to 400°F (200°C).
02 - Place each chicken breast between two sheets of parchment paper and pound with a meat mallet until approximately 3/8 inch thick.
03 - Season the flour with salt and pepper. Lightly dredge each flattened chicken breast in the seasoned flour, shaking off any excess.
04 - In a large oven-proof skillet, heat olive oil and butter over medium-high heat. Add the chicken and sauté for 2 to 3 minutes per side until golden brown. Remove the chicken and set aside.
05 - In the same skillet, sauté the finely chopped shallot until softened, about 2 minutes. Pour in the dry white wine and let it reduce by half. Add the crushed tomatoes and dried oregano; simmer for 5 minutes. Adjust seasoning with salt and pepper if needed.
06 - Return the seared chicken to the skillet. Top each breast with a slice of prosciutto followed by a slice of Fontina cheese. Spoon a small amount of sauce over each portion.
07 - Transfer the skillet to the preheated oven and bake for 10 to 12 minutes, or until the chicken is cooked through and the cheese is melted and bubbly.
08 - Garnish with fresh basil leaves before serving. Serve hot, accompanied by crusty bread or sautéed greens.