Remove the central cartilage from the chicken breast by dividing it in half and then cut cubes of about 2-3 cm from the meat. Keep it aside.Clean the mushrooms by removing the underside, rinse them quickly under running cold water, dry them and cut them into slices of about half a centimetre, following the shape of the mushroom.In a pan with a wide bottom, melt the butter with the oil over low heat, add the chopped aromatic herbs and crushed garlic. Cut the carrots and celery into very small cubes and put them together in a pan and brown them slowly for 10 minutes.In the meantime, flour the chicken cubes well and add them to the pan, raising the heat and browning for a few minutes, add the mushrooms and wait another 2-3 minutes stirring, then blend it with the white wine, let it evaporate and add the vegetable broth leaving everything cooking for about 15-20 minutes on a low heat until the sauce has set. Stir occasionally in the meantime. As soon as the stew is ready, add salt and pepper to taste and serve hot.