2) In a large Dutch oven, heat 2 tbsp olive oil over a medium heat. Add the roast and sear for 4 to 5 minutes, until nicely browned. Turn and sear the other side and then turn and sear the ends. This should take 4 to 5 mins for each side. Remove the roast to a large plate.
3) Add 2 tbsp olive oil to the Dutch oven. Add the carrots, onions, celery, leeks, garlic, 1 tbsp salt and 1 1/2 tsp pepper and cook over medium heat for 10 to 15 mins, stirring occasionally, until tender but not browned.
4) Add the wine and Cognac and bring to a boil. Add the tomatoes, chicken stock, bouillon cube, 2 tsp salt and 1 tsp pepper. Tie the thyme and rosemary together with kitchen string and add to the pot. Put the roast back into the pot, bring to a boil, and cover.
5) Place in the oven for 2 1/2 hrs, until the meat is fork tender or about 70°C internally. Turn the heat down to 120°C after about an hour to keep the sauce at a simmer.
6) Remove the roast to a cutting board. Remove the herb bundle and discard. Skim off as much fat as possible from the sauce. Transfer half the sauce and vegetables to a blender or a food processor fitted with the steel blade and puree until smooth.
7) Pour the puree back into the pot, place on the stovetop over low heat, and return the sauce to a simmer. Place 20g flour and the butter in a small bowl and mash them together with a fork. Stir into the sauce and simmer for 2 mins, stirring until thickened. Taste for seasonings. Remove the strings from the roast, and slice the meat. Serve warm with the sauce spooned over it.