Generously season the short ribs with salt and pepper. For added flavor season with thyme and/or rosemary.
Preheat the oven to 275 degrees F
In a large Dutch oven, over medium-high heat, heat oil, and butter. Working in batches, sear short ribs on both sides. About 3 minutes on each side or until nicely browned. Transfer short ribs to a plate using tongs.
Add diced carrots, onion, celery, and garlic to the Dutch oven. Mix with a wooden spoon or spatula picking up all the brown bits from the bottom of the pan. Cook for several minutes until the onion softens.
Add wine, mix with spoon or spatula, cook for 3-4 minutes to burn off the alcohol and reduce the liquid. Add mustard and stir to combine. Using tongs, return the short ribs back into the Dutch oven including all the juices that accumulated. Add enough stock and or water to cover the meat about ⅔ of the way. Season with salt (skip this if using store-bought stock that is already salted). Add a small bunch of fresh parsley for added flavor. Bring to a simmer, cover with a lid and put into the oven, on the middle rack.
If just making the short ribs cook for about 3.5 hours or until the short ribs are fork-tender and falling off the bone. If making a one-pot meal (with potatoes and carrots) cook for 2 to 2.5 hours and follow the next steps.
Remove from the oven (make sure to use oven mitts), add potatoes, chopped carrots, gently mix and make sure vegetables are submerged in liquid. Close the lid and return to the oven for another hour. Plate and serve the short ribs with potatoes and carrots, sprinkled with some fresh parsley.
Or another option (if you have time and want to take it to the next level) is to remove the extra fat and reduce the sauce. Let the pot cool off and refrigerate it (this will help the fat rise for easy removal). When ready to serve, remove and discard the top fat layer with a slotted spoon. Put the dutch oven back on the stovetop over medium heat and reheat. Using tongs, remove potatoes, chunky carrots, and short ribs from the pot into a plate or container. Turn the heat to medium-high and cook down the sauce until it is reduced and thickened, about 7 minutes.
Plate and serve potatoes, carrots and short ribs with sauce and garnish with gremolata, a mixture of lemon zest, fresh garlic, and chopped parsley.
Notes
When purchasing the short ribs, ask the butcher for the thickest, meatiest ones they have as they will shrink during the braising process. For the wine, red is preferred. But most importantly, use wine you would actually drink.