Heat a roasting pan over high heat with the oil. Sprinkle the ribs with salt and pepper. Add the ribs to the pan, then reduce the heat to medium. Sear on both the top and bottom of the meat, 2 to 3 minutes per side, reserving the pan drippings. After searing the ribs, add the stock, mirepoix, tomato paste, merlot, garlic and the reserved pan drippings to the pan. Tightly cover and cook in the oven for 2 1/2 to 3 hours. Remove the pan from the oven and check the ribs, which should be fork tender. If need be, continue cooking to achieve desired tenderness. Next remove the ribs and reserve the liquid to create sauce.
Pour the reserved cooking liquid through a strainer, then discard the remaining vegetables. In a saucepan, blend the herbs and liquid over medium-high heat. Reduce the liquid by three-quarters, yielding 3 cups of sauce. Pass the reduced sauce through a strainer, then set aside and keep warm.
For the potatoes: In a large pot, bring 1 gallon of water to a boil. Add the potatoes and cook until softened, 15 to 18 minutes, then drain. Pass the potatoes and butter through a food mill or ricer into a bowl. Next add the salt and pepper, and then blend with a whisk. Taste and add additional salt and pepper if needed.
To serve, place the mashed potatoes in the center of the plate, top with a short rib, and finish with the warm sauce. Repeat for the remaining short ribs.