Slow Cooker London Broil is moist and tender, and super easy to make. It will quickly become your favorite meat and potatoes meal to make.
First, pat dry beef with paper towels and season with salt and pepper on each side.
Place a large cast iron pan or Dutch oven on the stove over medium-high heat. Once hot, add oil, and sear beef on all sides for about 1-2 minutes on each side, until golden brown in color.
Transfer the meat to an 8 qt slow cooker. Add the rest of the ingredients, except carrots and potatoes, and adding the butter last on top of the beef. Gently stir to combine.
Put the lid on the crockpot and cook for 5-6 hours on high, or 8-10 hours on low.
If you want to add carrots and potatoes, add them to the slow cooker when there are 2-3 more hours of cooking left. Cover and continue cooking until tender.
Combine cornstarch and water in a small bowl until cornstarch is fully dissolved. Add the mixture to the slow cooker when one hour of cooking is left. Gently stir. This will thicken the gravy. Check after 30 minutes, and if needed add more.
Once done, transfer the London Broil on a serving platter and carve. Arrange the potatoes and carrots around the roast. Garnish with fresh chopped parsley and drizzle with the gravy before serving.