Ingredients :

• Chicken breasts — Choose them of similar size if you can. If one is significantly thicker than the others, flatten it with a rolling pin—it changes everything for even cooking. A breast that’s too thick cooks twice as slowly as a thin one, and you’ll end up with dry meat on one side and pink on the other.
• Apple cider vinegar (or red wine) — This is what brings the tangy touch and slightly tenderizes the meat. Apple cider vinegar is milder and fruitier, red wine is sharper and bolder. Both work well. Avoid balsamic; it’s too sweet and would burn on the grill.
• Worcestershire sauce — Three tablespoons that seem harmless but make a real difference. It brings an umami depth that’s hard to describe—savory, slightly caramelized. Don’t replace it with soy sauce; it’s really not the same thing.
• Dijon mustard — It does two things at once: it binds the marinade so it sticks well to the chicken, and it adds a pungent-sweet taste that pairs perfectly with the herbs. Use real Dijon mustard—not yellow hot-dog mustard.