Method:

1. Toast peppercorns, coriander, fennel, chiles de àrbol, and bay leaves in a small skillet over high heat, stirring occasionally, until fragrant, 2 to 3 minutes. Transfer aromatics to a hard surface; lightly crush with the bottom of a heavy skillet; then transfer to a 9"x13" baking dish.
2. Add wine, vinegar, worcestershire, garlic, rosemary, and olive oil; whisk to combine. Poke flank steak all over with a fork and place in marinade; spoon some marinade over top. Cover and refrigerate, turning occasionally, for 12 to 24 hours.
3. An hour before grilling, transfer steak to a plate; set aside at room temperature. Transfer marinade to a small pot and bring just to a boil; set aside.
4. Build a medium-hot charcoal fire in your grill. Grill steak, turning once and, using a brush, basting with reserved marinade occasionally, until browned and medium rare, 7 to 8 minutes per side. Transfer to a cutting board, tent with foil, and let rest for 10 minutes. Carve steak into thin slices on the bias and serve with any accumulated juices.