Preheat oven to 190ºC . Cook potatoes in skins, done but firm. Peel and slice crosswise half in. thick.Oil large shallow baking dish. Alternate potatoes and tomatoes in rows. Drizzle lightly with olive oil, sprinkle with rosemary, chives, salt and pepper. Bake 20 to 25 min, or until potatoes begin to turn golden crisp around edge.