1. In a large pot, heat the unsalted butter, olive oil, or plant butter over medium heat until melted.
2. Add the sliced leeks and sauté for 5-7 minutes until soft and fragrant.
3. Stir in the minced garlic and cook for another 1-2 minutes until aromatic.
4. Add the chopped cabbage and diced potatoes to the pot, stirring to combine.
5. Pour in the vegetable broth and add the tied thyme springs.
6. Bring the soup to a boil, then reduce heat to low and simmer uncovered for 25-30 minutes, until the potatoes and cabbage are tender.
7. Remove the thyme springs and stir in the cooked cannellini beans.
8. Season with fine sea salt, fresh ground pepper, and a squeeze of lemon juice to taste.
9. Simmer for an additional 5 minutes to heat through.
10. Serve hot garnished with shaved Parmesan cheese if desired.