Franciacorta, Italy — On a moonlit night in Milan, Italy’s most elegant oenophiles are mingling in a 19th-century mansion. In a sweeping tide of satin, silk and slim-cut suits, they swarm the marble staircase, check their reflections in smoked-glass mirrors, and get jiggy on a parquet dance floor, all the while juggling magically-refilling glasses of bubbly.