To make the short ribs fit in the crock pot, trim them into smaller pieces if necessary. On all sides, generously season the meat with salt and pepper.
Cut the garlic and onions into slices. In a pan, heat the oil over medium-high heat. After sautéing the onions for two to three minutes, add the garlic and continue to cook for one more minute. Take out of the pan.
The short ribs should be added to the same pan and seared on high until browned on both sides.
Place the seared short ribs in the crock pot together with the fresh rosemary, onion, and garlic, as well as the beef stock and Worcestershire sauce.
Cook for four hours on HIGH or seven hours on LOW.
Take out of the crock pot the cooked short ribs. Sort the leftover mixture through a sieve into a big saucepan, leaving the liquid alone.
Cornstarch should be dissolved in a little amount of water or cooking liquid to create a slurry. After that, mix the slurry into the cooking liquid in the saucepan over medium heat until the required thick consistency is reached.
Optional step: Put some gravy in a baking dish, then arrange the short ribs on top if you want them to get a bit crisp or char. Before serving, cook for a few minutes under the broiler.