The evening before, cut the beef into large chunks and place in a large bowl.
In a cast iron pot, Dutch oven or an electric slow cooker, heat the olive oil and sweat the shallots and onion over medium heat.
Add the smoked pork belly, and sauté for 3 minutes over medium heat. Add the meat, and brown the pieces of beef on each side.
Remove the celery and leek from the marinade and add the marinade to the pot. Cook 1 minute over high heat and simmer over very low heat for 5 to 7 hours or more.