3 tablespoons coarsely chopped fresh rosemary, plus sprigs for garnish
1/4 cup plus 2 tablespoons Worcestershire sauce
2 tablespoons extra-virgin olive oil, plus more for brushing
Freshly ground pepper
1 3/4 pounds skirt steak
1 1/2 pounds small red potatoes
3 ounces blue cheese, crumbled
Preheat grill to high. Stir garlic, rosemary, Worcestershire sauce, and oil in a nonreactive dish; season with pepper. Place steak in dish, cutting to fit if necessary; coat both sides with marinade. Marinate, turning once, 15 minutes, or up to overnight in the refrigerator.
Cover potatoes with cold water in a medium saucepan; add a pinch of salt. Bring to a boil. Reduce heat, and simmer until just tender, about 15 minutes. Drain; let cool slightly. Slice potatoes in half, and brush lightly with oil; season with salt and pepper.
Grill steak, turning once, to desired doneness, 3 to 4 minutes per side for medium-rare. Set aside. Meanwhile, grill potatoes, turning once, until lightly browned, about 5 minutes. Immediately sprinkle with cheese. Thinly slice steak against grain. Divide steak and potatoes among 4 plates. Serve, garnished with rosemary sprigs.