It sounds like the fanciest entrée at the best restaurant in town, but actually Grilled London Broil is an inexpensive and delicious way to feed a large family or a backyard full of hungry guests. The marinade does most of the work for you and the coals do the rest for perfect results every time.
Cut 1/2-inch crosshatch pattern, 1/4 inch deep, on both sides of steak. Place steak in 1-gallon zipper-lock bag.
Combine soy sauce, vinegar, ketchup, sage, garlic, oil, and rosemary in blender and process until garlic and herbs are finely chopped, about 30 seconds.
Add marinade to a bag with steak, seal and turn to coat. Let sit at room temperature for 2 hours or refrigerate for up to 8 hours. (If refrigerated, bring the steak to room temperature before grilling.)
To prepare a charcoal grill:
Open bottom vent completely. Light large chimney starter filled with charcoal briquettes (6 quarts). When top coals are partially covered with ash, pour evenly half of the grill. Set cooking grate in place, cover, and open lid vent completely.Heat grill until hot, about 5 minutes.
To prepare a gas grill:
Turn all burners to high, cover, and heat grill until hot, about 10 to 15 minutes.
To grill the steak:
Combine pepper and paprika in a bowl. Remove steak from marinade, pat dry with paper towels, and season with pepper mixture.
Clean and oil cooking grate. Grill steak (hotter side of grill if using charcoal) for 1 minute. Flip and grill second side for 1 minute. Repeat, flipping every minute, until steak registers 125 degrees (for medium-rare), 5 to 7 minutes, or 130 degrees (for medium), about 9 minutes.
Transfer to carving board, tent loosely with aluminum foil, and let rest for 10 minutes. Slice steak thinly against the grain and serve.