Puntarelle are the inner hearts of cicoria catalogna, a kind of chicory — and one of the greatest treats of springtime in Rome. The hearts are trimmed out of the large heads and cut into thin shreds that curl up when immersed in ice water. Since puntarelle are not easy to find in this country, a mix of Belgian endive and celery serves as a wonderful substitute: Together, they have the same addictive bittersweet-crisp quality.