Fry the onions in olive oil till caremalized. Add the eggplant and tomato (if you use fresh then grate it and discard skin) also add a pinch of sugar to cut the acidity of the tomato. Salt & pepper to taste and add bay leaf. Cook on low until soft and melted together. If you have to add liquid use wine. After you turn off the heat, add the vinegar immediately. Stir it in, let sit for about a minute and then serve with a good bread.