Heat a little butter or olive oil in a frying pan on low - medium heat.
Fry onions for a few minutes, then add carrot and garlic and fry until cooked (about 3-5 minutes)
Add apple cider vinegar and cook for about a minute.
Add beans, tomato puree and water. Stir to combine.
Simmer for another 5 - 10 minutes, until sauce has reduced and beans are tender.