Frank Galati is a noted specialist in the work of Gertrude Stein: he’s directed the Stein-Virgil Thomson operas The Mother of Us All and Four Saints in Three Acts for Chicago Opera Theater, and his 1987 tribute to Stein and Picasso–She Always Said, Pablo, produced by the Goodman–lingers in my memory as one of the most mesmerizing productions I’ve ever seen. In this one-act chamber musical–receiving its world premiere at Northwestern University, where Galati teaches–Galati and composer Stephen Flaherty (whose Ragtime Galati staged on Broadway) offer a brisk, ebullient introduction to the life and work of Stein, who as writer and cultural maven exerted a profound influence on modern art and literature. Dispelling her image as an inaccessible avant-gardist, A Long Gay Book reveals her wit and charm and sweetly celebrates her lifelong relationship with Alice B. Toklas. As usual, Galati’s stage pictures are beautifully composed, and his pleasure in the refined elegance of Stein’s era–the late 19th and early 20th centuries–is palpable. But his characterizations of Stein and Toklas are shallow and idealized–and strangely asexual considering the show’s forthright acknowledgment of the lesbian subtext of Stein’s work. Flaherty’s score doesn’t come close to the brilliant music her writing inspired from Thomson in the 30s and 40s or from off-Broadway songwriter Al Carmines in the 60s and 70s. But this pretty pastiche of rag, blues, tango, sentimental ballads, and other period idioms is nicely matched to Stein’s lean, repetitive, incantatory texts. The production is charmingly choreographed by Marc Robin and beautifully designed–kudos to costumer Michelle Tesdall for her creamy dresses and suits. And the cast, a mix of students and professionals, is first-rate, especially Christine Mild as the young Gertrude. Northwestern University Theatre and Interpretation Center, Ethel M. Barber Theatre, 1949 Campus Dr. (enter at 30 Arts Circle Dr.), Evanston, 847-491-7282. Through May 18: Thursday-Saturday, 7:30 PM; Sunday, 2 PM. $11-$24.