• Combine all the ingredients for the marinade. Remove ¼ cup of the marinade and reserve for later if you want to make gravy. Place the rest of the marinade in a resealable plastic bag.
• Add the London Broil to the bag. Seal the bag and place it in the refrigerator for 6 to 10 hours. 
• Preheat the pellet grill to 200°F. 
• Remove the London Broil from the marinade and pat it dry with paper towels. Discard the marinade that the meat was soaking in.
• Place the roast directly on the grill grates. 
• Smoke for 50 minutes then turn the heat up to 450°F.  Cook for an additional 10 to 35 minutes or until an internal meat thermometer reads 125°F for rare, 132°F for medium rare, or 138°F for medium. The cooking time will vary depending on the thickness of the meat. 
• Let the roast rest for 15 minutes the slice it as thin as possible. Make sure you slice the meat against the grain. 

For the Gravy

• Melt the butter in a saucepan or skillet over medium heat. Whisk in the flour and stir for 1 minute. 
• Slowly pour in the broth, about ¼ cup at a time, while whisking constantly. Whisk until the mixture gets smooth before adding more broth, then repeat until all the broth is added.
• Add the ¼ cup of reserved marinade, pepper, and salt. Simmer for 3 to 5 minutes, stirring continuously until thickened. 
• Remove from heat and add additional salt and pepper if desired. Serve with the London Broil.