Gently poach chicken breasts so they come out tender, juicy, and easy to shred — never rubbery.
Place chicken breasts in a single layer in a pot and add cold water or chicken broth until they are covered by about 1 inch. Broth and aromatics (a smashed garlic clove, half an onion, a bay leaf, salt and pepper) add flavor.
Heat over medium-high just until you see small bubbles starting to break the surface, then immediately reduce the heat. A hard rolling boil toughens the meat — you want a gentle poach, not a boil.
Keep the liquid at a bare simmer and cook boneless breasts for 12-15 minutes (longer for thicker pieces or bone-in). The chicken is done at an internal temperature of 165°F at the thickest part.
Remove the chicken and let it rest 5 minutes so the juices redistribute, then slice or shred with two forks. Save the cooking liquid as a light stock for soups or rice.