Preheat the oven to 200 degrees Celsius (390 degrees Fahrenheit)
Season the short ribs on all sides with salt and pepper. Heat the olive oil on high heat in a large oven proof pot and then sear the short ribs for 3-4 minutes per side until browned. Once they are seared on all sides transfer them to a plate and set aside.
Add to the pot the onion, leek, garlic and carrots and cook for 5 minutes until the veggies begin to soften. Next add in the tomato paste, balsamic vinegar, beef stock, thyme, chopped tomatoes and bay leaves and bring the mixture to a boil.
Once boiling, return the short ribs back to the pot cover with a lid and place in the oven to cook for 2 1/2-3 hours until the meat is fall of the bone tender.
Once the meat is done cooking, return the pot to the stove top. Remove the short ribs from the pot and set them aside on a plate. Bring the pot to a boil and let it cook on high heat for 10 minutes until the liquid has reduced by half.
At this point you can serve the sauce as it, or alternatively using an immersion blender, remove the pot from the heat and blend the sauce until its completely smooth.
Serve the short ribs with the sauce and a side of mash
Season the short ribs with salt and pepper. Brown the meat on all sides in olive oil using the sear function. Set aside
Add to the pot the onion, leek, garlic and carrots and and cook for about 5 minutes until the veggies begin to soften.
Next add in the tomato paste, balsamic vinegar, beef stock, thyme, chopped tomatoes and bay leaves and return the short ribs to the pot. Cook on high pressure for 40 minutes.
When finished cooking use the natural release for 10 minutes. Remove the meat from the pot and use the saute function to reduce the liquid by half. Serve the sauce as is or use an immersion blender to blend into a thicker sauce. Serve the short ribs with the the sauce poured over top and a side of cauliflower mash.