Braised Green Beans and Potatoes in Tomato Sauce

Stringless green beans (probably the only kind you can get in the United States) became widely available in Greece only in the last few years. As far back as I can remember, before we could cook this very popular summer dish, we had to slave for hours trimming each one of the flattish beans—a kind of runner bean—that we cooked. Tender green beans are so much easier to prepare, but their taste lacks the meatiness of those old beans we called barbounia—“red mullet,” likened to the dain