Clare Cosi’s new friend, millionaire David Mintzer, has an offer no New York barista could turn down: an all-expenses-paid summer away from the sticky city. At his Hamptons mansion, she’ll relax, soak up the sun, and, oh yes, train the staff of his new restaurant. So Clare packs up her daughter, her former mother-in-law, and her special recipe for iced coffee—for what she hopes will be one de-l...