01 - Preheat your oven to 400°F (200°C).
02 - Place the chicken breasts between two sheets of parchment paper and flatten using a meat mallet until about 1/2 inch thick.
03 - Season the flour with salt and pepper. Lightly dredge each 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 2–3 minutes per side until golden brown. Remove the chicken and set aside.
05 - In the same skillet, add the finely chopped shallot and sauté until softened, about 2 minutes. Pour in the dry white wine and let it reduce by half. Stir in the crushed tomatoes and dried oregano, then simmer for 5 minutes. Adjust seasoning with salt and pepper as needed.
06 - Return the chicken to the skillet. Top each breast with a slice of prosciutto and a slice of Fontina cheese. Spoon a little sauce over the top of each piece.
07 - Transfer the skillet to the oven and bake for 10–12 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, preferably with crusty bread or sautéed greens.