Thinly slice your beef and chop your onions, and add to a large mixing bowl
Dice the pear and add it to a blender, along with the soy sauce, sesame oil, brown sugar and crushed garlic cloves. Whizz until smooth. Pour the marinade over the beef, and combine until the marinade is evenly distributed.
Cover and leave in the fridge overnight (or at least 4 hours if you're short on time)
Take the beef out 20 minutes prior to cooking. Heat a skillet or barbecue on medium-high heat and add the cooking oil.
Add the beef and onions in a single layer and quickly sear until cooked to your liking. Do not overcrowd the pan or add any excess liquid from the marinade- the beef will go soggy rather than caramelising. You may need to cook the beef in several batches
Once the beef is cooked, set aside and sprinkle over with the toasted sesame seeds, tossing until the beef is evenly coated