Preheat oven to 300° F.
Pat the beef dry and season generously on all sides with salt and pepper. Sprinkle all over with all purpose flour and pat it into the meat on all sides.
Pour oil into a dutch oven and heat over medium-high until the oil shimmers. Once hot, sear the meat for about four minutes per side, or until nicely browned all over. Set it aside to rest on a plate.
Reduce the heat to medium and, if necessary, add a touch more oil to the pan. Add in the leeks an onion and sautee for about three minutes, or until they begin to sweat and soften. Add in the garlic and sautee for another two minutes.
Stir in the tomato paste and dijon mustard. Add in the wine, Worcestershire sauce, and beef broth. Stir until well combined and bring to a boil. Drop in the bay leaf, thyme and rosemary. (You can tie the herbs together for easier extraction at the end.)
Reduce the heat to a simmer and return the roast and all of its pan juices to the pot. Cover with a tight fitting lid and transfer to the preheated oven to slow cook for three hours.
After three hours, remove the pot from the oven and taste the sauce. Add more salt and pepper if necessary. Then, add in the potatoes and carrots, nestling them into the sauce around the roast. Cover and return to the oven for another hour, or until the vegetables are tender.
Serve and enjoy! I like to eat mine with buttered crusty sourdough to sop up all the juices.