Heat oil in a large stock pot and add onions and garlic. Cook until fragrant and onions are clear. Add chopped potatoes and beef broth.
Cover pot and bring to a boil on medium heat. Cook 20-25 minutes or until potatoes are nice and soft, almost mushy.
Add cabbage and cook another 5-7 minutes until cabbage is tender. Break up canned corned beef into crumbles and add to soup. It will break up even more once it is in the broth and distribute through the soup.
Heat through then serve.
Notes
Soup reheats well for leftovers and can be stored in the refrigerator for up to 5 days.