Rocco DiSpirito is back with his first Big Apple restaurant in six years  — and it’s about time. Bar Rocco (32 W. 48th St.) is a proudly old-school Italian American restaurant on the Kimpton Era Hotel’s second floor. It’s plain wonderful, thanks to DiSpirito’s skills, which first wowed the city at French-American Union Pacific in the late 1990s. It also makes use of better ingredients than ordinary red-sauce places. DiSpirito’s last gig in the city was at the Standard Grill. He was there for