Flatten a couple of skinless chicken breast fillets between two sheets of cling film, using a meat mallet, to make nice thin escallops.
Dredge with seasoned flour and sauté in melted butter over a medium heat, until browned on both sides. Transfer to a shallow baking dish.
Sauté sliced mushrooms and a chopped banana shallot until lightly browned, then pour in a half glass of white wine (or dry vermouth).
Bring to a boil and simmer for a few minutes, then pour the mixture over the chicken. Cover and bake in a 180°C oven for 10 minutes,
uncover and sprinkle with grated Gruyere cheese. Continue baking uncovered for another 10 minutes or so, until the cheese is browned and bubbly.