Add 2 tablespoons olive oil to the Dutch oven. Add the carrots, onions, celery, leeks, garlic, 1 tablespoon salt, and 1 1/2 teaspoons pepper and cook over medium heat for 10 to 15 minutes, stirring occasionally, until tender but not browned. Add the wine and Cognac and bring to a boil. Add the tomatoes, chicken stock, bouillon cube, 2 teaspoons salt, and 1 teaspoon 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. Place in the oven for 2 1/2 hours, until the meat is fork tender or about 160 degrees F internally. Turn the heat down to 250 degrees F after about an hour to keep the sauce at a simmer.