Drizzle over the vinegar, then the olive oil, and season with pinches of sugar, sea salt and ground black pepper. Bake for 30 mins, covered, until the peppers are tender and collapsing a little. Remove, uncover and cook for a further 30 mins. Leave the peppers to cool a little, then scatter with parsley, if you like, and spoon onto plates, scooping out any extra juices. Serve with crusty bread for mopping up the juices.