Preheat the oven to 200°C (180°C Fan/Gas 6).
Mix the cream cheese with garlic, herbs, salt, and pepper.
Cut a pocket into each chicken breast and fill with the cream cheese mixture.
Wrap each chicken breast with Parma ham.
Sear the chicken in olive oil until lightly golden on both sides.
Roast the potatoes, onions, garlic, and ham pieces for about 25 minutes.
Add mushrooms, white wine, chicken stock, cream, and Reblochon cheese.
Place the wrapped chicken on top and bake for another 20–25 minutes, or until fully cooked.
Stir in the mustard, lemon juice, and remaining herbs.
Rest the chicken for a few minutes, slice if desired, spoon over the creamy sauce, and serve hot.