Prep the aromatics: Stud the halved onion with the cloves. Cut the carrots and celery into large chunks. Tie the parsley stems, thyme sprigs, and bay leaves into a bouquet garni.
Set the chicken breast-side up in a large, deep pot. Add the onion, carrots, celery, bouquet garni, peppercorns, wine, and salt.
Pour in the cold water (it should cover or nearly cover the chicken). Bring slowly to just below a simmer over medium heat, 25–30 minutes, skimming any foam that rises. Aim for small, lazy bubbles (170–180°F/77–82°C); do not boil.
Adjust heat to maintain a bare simmer, cover partially, and poach until the thickest part of the thigh (not touching bone) registers 165°F/74°C and the juices run clear, 35–45 minutes. Rotate the chicken once halfway if needed for even cooking.
Lift the chicken from the pot, letting excess liquid drain back, and rest on a platter for 15 minutes to allow juices to settle.
Strain the poaching liquid through a fine-mesh sieve; reserve as a light broth and keep hot or cool for storage, skimming fat if desired.
Carve the chicken and serve warm with some of the hot strained broth spooned over, or cool the meat for later uses.