A well-established rapport between client and designer is always a bonus, but when the two are dear friends there’s bound to be magic. So when interior designer Noah Ruttenberg’s high school friend Eugenia Zobel de Ayala asked him to renovate her Upper East Side apartment , he couldn’t wait to embark on their first collaboration together. “It’s such an amazing opportunity to work with someone you know deeply and with whom you’ve gone through various stages of life,” says the designer. However, the apartment—located in an early-20th-century building by architect George F. Pelham —had already seen plenty of life. Despite its good bones, the residence would require a major rethink to meet the wishes of Zobel de Ayala and her husband.

The living room is broken into multiple zones. The dining area features a custom banquette upholstered in a Pierre Frey linen, a table covered with a Suzani textile, and vintage lacquer chairs by James Mont.…