Peel and with a sharp knife, slice the onions thinly, about 1/8-inch thick slices.

Heat the olive oil in a large, heavy-bottomed skillet over medium-low heat.

Once the oil is hot, add the sliced onions along with a pinch of salt and black pepper. Stir them well.

Stir the onions every few minutes, scraping up any bits that stick to the pan. Cook for about 15 minutes.

When the onions are soft and golden brown, stir in water, balsamic vinegar, and sugar. Let it cook for another 20 minutes with the lid on, stirring often, and add more water if needed.

Taste your caramelized onions. They should be sweet, rich, and slightly sticky. Adjust seasoning with more salt or vinegar if needed.

Let the caramelized onions cool before transferring to an airtight container or serving.