Heat the oil on high in a large frying pan (or using the searing function of your slow-cooker if it has one). Place the short ribs in the pan and brown on all sides. This should take about 10 minutes.
Add in the onion and cook for a further 2 minutes, whilst stirring.
Add in the garlic and heat through for a minute, then add in the red wine.
Bring to a bubble and allow to simmer for 3 or 4 minutes, then add in the rest of the short rib ingredients.
Stir together and bring to a simmer, then transfer to the crockpot. Place the lid on and cook on low for 6-8 hours.
To make the gravy, ladle most of the cooking liquid out of the slow cooker and into a saucepan.
Heat the sauce over a high heat until bubbling.
Mix the cornstarch and water, then slowly pour the mixture into the cooking liquid whilst whisking - until the gravy thickens. You may not need all of the cornstarch. You’re looking for a nice gravy of a medium-thick consistency.
Turn off the slow cooker and place one short rib on top of a pile of mash. Pour over a little gravy, and repeat with the other 3 short ribs. Serve with steamed green vegetables.