The evening before, put the chickpeas in a bowl with plenty of cold water (they must soak for at least 12 hours). The following morning, strain them, then put them in clean cold water and bring to the boil over a moderate heat with a pinch of coarse salt, a tablespoon of extra virgin olive oil, the sprig of rosemary and the whole clove of garlic. Boil for at least two hours, and when they are well cooked, strain them. Put the chick peas – warm or cold – in a large bowl (or several small bowls for individual portions) with the onions (cleaned and thinly sliced), add the olive oil, vinegar, some salt, freshly ground pepper and the chopped parsley. Mix well and serve.