Preheat the oven to 325 and place a rack in the center of the oven. Season your shanks with salt and pepper. Heat a dutch oven over medium high heat and add a little olive oil. Brown the shanks on both sides in the dutch oven. About four minutes on each side. Remove from pan, and drain off all but about two tablespoons of oil.
To the dutch oven, add the onion, carrots and celery. Lightly season with salt and pepper and cook about four minutes. Add your tomato paste, demi glace (if using), garlic cloves and thyme, and cook for an additional three minutes. Add the red wine (not the port) and the shanks back to the dutch oven and bring to a simmer. Once simmering, cover and put in the oven. Braise for about 3 hours.
Meanwhile, pour all of the port in a saucepan and boil until it is reduced by ¾. You're looking for a thick, almost syrupy consistency.
When the the shank is finished, strain the sauce from the vegetables and shank. Pull the shanks out and set on a cutting board. When they have cooled slightly, shred the beef, it will be so tender that this will take almost no effort.
Pour the sauce back into the dutch oven and add the vegetables and any marrow out of the bone back to the pot. Using an immersion blend, puree the vegetable with the cooking liquid - this is what will thicken the sauce.Alternatively you can put the strained cooking liquid, the vegetables and marrow in a blender and puree, then add this back to the dutch oven.Gently rewarm on low heat on the stove top.
Add the reduced port wine syrup and stir in the shredded/pulled beef shank meat. heat all the way through.
Toss with pappardelle, gnocchi or pasta of choice, or spoon on top of polenta.
Notes
The ragu can be made and portioned into containers to freeze for up to three months. Thaw before reheating.Unfrozen the sauce can be refrigerated for up to five days before using.