01 - Preheat oven to 400°F (200°C).
02 - Place chicken breasts between two sheets of parchment paper and flatten using a meat mallet until approximately 3/8 inch thick.
03 - Season the flour with salt and pepper. Lightly dredge each 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 golden brown. Remove and set aside.
05 - In the same skillet, sauté the finely chopped shallot until softened, about 2 minutes. Pour in the white wine and reduce by half. Add the crushed tomatoes and dried oregano, then simmer for 5 minutes. Adjust seasoning to taste.
06 - Return the chicken to the skillet. Layer each breast with a slice of prosciutto and a slice of Fontina cheese. Spoon a small amount of sauce over the top.
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. Serve hot alongside crusty bread or sautéed greens.