While most pot roast recipes use white flour to thicken the sauce, I like to puree the cooked vegetables to create a thick and satisfying gravy to serve with the roast.
Pat the beef dry with a paper towel and season with the salt and pepper. Place the oil in a Dutch over and heat over medium heat. Add the roast and brown on all sides, about 10 minutes.
Place the onion, carrots, celery, leeks and garlic in a slow cooker. Place the roast on top of the vegetables, then add the tomatoes and their juices, the Chicken Broth, and wine. Tie the thyme and rosemary together with kitchen twine and add to the pot. Cook on low for 8 hours, basting the meat twice to keep it moist on top.
Transfer the roast to a cutting board and remove the twine. Slice the meat against the grain or shred with two forks.
Discard the thyme and rosemary and skim off the top layer of fat from the sauce. Transfer half the sauce, all the onion, and half of the other vegetables to a blender and puree until smooth.
Pour the gravy back into the pot and return the meat to the pot. Continue cooking on low for another 1 to 2 hours.
Adjust salt and pepper as needed. Serve hot with extra gravy on the side.