Heat oil in a large pan over medium to high heat. Add onions, garlic and sea salt and cook, stirring occasionally, for about 10 minutes until soft. Remove onions from the pan, add the chicken and fry, turning pieces to brown evenly.
Put the onions back in, add wine and cook until wine reduces to a couple of tablespoons.
Add tomatoes with their juice, chicken stock, olives, bay leaf and rosemary. Reduce heat to low, and simmer for 30-40 minutes.
The chicken should be cooked but not falling off the bone, and the sauce should have thickened. Check the seasoning, add a good grind of pepper and fold the vinegar through.