If the london broil doesn’t fit to the crockpot, you can slice it into little pieces. Then, season the meat with salt and pepper generously on both the sides of the meat.

Put the minced garlic and sliced onions in the bottom of slow cooker. Then, put the seasoned broil on top of the onions.

In a bowl, mix soy sauce, beef broth, dried thyme, balsamic vinegar, Worcestershire sauce, black pepper, dried rosemary and red pepper flakes. Mix them all until well combined.

Now, pour the sauce all over the london broil in the crockpot by ensuring that the meat is evenly coated.

Place a lid on the crockpot and let it cook over low heat for 6-8 hours or over high heat for around 3-4 hours. The cooking time may vary according to the thickness of the London broil and your crockpot.

About halfway through cooking, inspect the meat to check it’s doneness. Make sure to cook the London broil to medium-rare to medium for better flavor and texture. For this, you can use a meat thermometer to measure the internal temperature that should be around 135 F (57 C) for medium-rare and 145 F (63 C) for medium.

If you want a thicker sauce, mix cornstarch with water until it is smooth to prepare a slurry. Add the slurry to the crockpot in the last hour of cooking and mix it well. It will make the sauce thicker.

Once the London broil is cooked as per your level of doneness, take it out from the crockpot and allow it to rest for few minutes before slicing it.

It’s time to serve the London broil with sauce and onions.