Heat milk with aromatics until bubbles form and infuse for 20 minutes.
Double coat chilled dariole moulds with melted butter, chilling between layers.
Soak bread in strained flavored milk for 20 minutes.
Preheat the oven to 180°C.
Truss the chicken with lemon and thyme and coat with softened butter.
Roast chicken for about 90 to 105 minutes while basting regularly.
Mix soaked bread with sautéed onion and beaten eggs, then spoon into moulds.
Bake puddings in a water bath with the chicken for 1 hour.
Rest chicken for 15 minutes and create a sauce with pan juices, wine, and tarragon.
Carve chicken and serve with the turned-out bread puddings and sauce.