Preheat the oven to 350°.
Add oil to dutch oven and heat until hot. Generously salt and pepper short ribs.
Add short ribs to pot and get a good sear on every side. This took about 10 minutes for 8 short ribs, 4 in each batch. You will be deglazing the pan later, so it's good if bits stick to the pan. You want an amber-brown color.
Remove short ribs and place in roasting pan or cast-iron skillet.
In the same pan, saute carrots and onions for 5 to 8 minutes. The Guinness recipe calls for celery and I didn't realize we were out, so I used celery seed. Add that to the carrots and onion. I think it was a great substitute, but you may want to use celery for the true recipe. Once vegetables are relatively soft, transfer to roasting pan.
Deglaze the pan with the Guinness Draught. Add juices to pan along with the beef stock, tomato juice, and thyme.
Cover tightly with foil and place in 350° oven for 2 1/2 hours.
Remove short ribs from pan and transfer to a plate to rest. Strain the liquid and divide in half. Pour half the liquid into a saucepan and reduce over medium/high heat to make a sauce.
When ready to serve, simmer the short ribs in the other half of the liquid until tender, about 15 minutes. Spoon the sauce reduction over the ribs.