1. Trim and wash the beans. Place them in a saucepan with water to cover, add a little salt and the savory, then cover the pan, bring to the boil and simmer for about 5 minutes, until the beans are tender.
2. Drain and leave to cool. Cut larger beans into halves or quarters.
3. Cut the onion into rings. Dice and fry the bacon until crisp, then mix it with the vinegar, salt and the cayenne. Mix the dressing into the beans with the onion rings.