Cut the leaves from the stems. Wash both stems and leaves very well.
Finely chop 1 onion, the stems and 3 cloves of garlic.
Fry the onion in a few tablespoons of olive oil until soft. Add the stems and the garlic. Cook for another 5 minutes.
Tightly roll the leaves together and finely slice.
Add them to the pan, cover and when the leaves wilt, add a little more oil.
Pour over 2 tablespoons of balsamic vinegar and toss well.