Preheat the oven to 325 degrees F. (163 degrees C.).
Place the meat on a cutting board and pat dry with a sheet of paper towel on all sides. Tie meat using kitchen twine. Season it with salt and pepper. Dredge the whole meat in flour, ensuring that all parts are covered with flour. Shake the excess flour.
Heat the oil over medium heat in a large Dutch oven. Cook the meat for 4-5 minutes on each side. Transfer it to a large plate, cover it with aluminum foil, and set it aside. Do not wash the Dutch oven.
Heat oil in the now-empty Dutch oven. Place chopped carrots, onions, celery, leeks, garlic, 1 tablespoon salt, and 1 teaspoon black pepper in the Dutch oven. Cook until all vegetables soften, 12-15 minutes, stirring often. You do not want the vegetables to turn brown.
Stir in the wine and cognac (if using), followed by tomatoes and chicken stock. Make an herb bouquet by tying thyme and rosemary. Place in the pan.
Transfer the roast back to the Dutch oven, bring it to a boil, and let it come to a simmer for 12-15 minutes.
Put the lid on and place it in the oven. Roast for 2 ½ hours, or the internal temperature registers 160 degrees F (72 degrees C.) when inserted with a digital thermometer. Next, turn the heat down to 250 F Degrees (or 122 degrees C) and let it simmer at that low temperature for an hour.
Carefully remove the pot roast onto a cutting board and cover it loosely with aluminum foil. Discard the bundle of herbs. Using a large spoon, skim off the fat on top of the juices as much as possible.
Transfer 3-4 cups of the sauce (about half of the sauce) and vegetables into a bowl and puree until smooth. I used an immersion blender but a food processor fitted with the steel blade or a standing blender would also work.
Pour the pureed sauce back into the pot. Put the Dutch oven on the stovetop, turn the heat on to medium-low, and return to a simmer for about 15 minutes.
Remove the strings from the roast and slice the meat.
When ready to serve, place 2 (or more) slices of meat on a dinner plate and spoon the vegetable sauce over it.