Put the beef in a large pan and cover with cold water.
Roughly chop the celery (reserve the leaves for later), then peel and cut the onions into 2.5cm wedges. Peel and slice the carrots at an angle into 5cm pieces, then cut the corn into chunks, roughly the same size. Peel and cut the sweet potatoes into 4cm chunks, then cut the cabbage into wedges.
Add the celery and onions to the pan, season with 1 teaspoon of sea salt and a generous pinch of black pepper, then gently bring to the boil. Reduce to a simmer, cover with a lid and leave to tick away for 2 hours.
After 1 hour 10 minutes, add the carrots and corn to the pan, then simmer for about 15 minutes, or until cooked. Remove with a slotted spoon and set aside.
Add the sweet potatoes to the pan and cook for the final 30 minutes, throwing in the cabbage halfway through.
Transfer the meat to a board, sprinkle over the oregano and leave to rest for a few minutes.
Return all the cooked veg to the broth and bring back to the boil to warm through. Divide the veg among your bowls and top with the broth. Slice and add the beef, then serve with the celery leaves scattered on top.