Relaxed, if quite often intense and exploratory, the previously unreleased On a Monday Evening captures pianist Bill Evans in a peak performance leading his trio circa the mid-‘70s, with virtuoso bassist Eddie Gomez and drummer Eliot Zigmund. The show at a packed 1,000-seat Wisconsin Union Theater on the UW-Madison campus survives, thanks to some serendipity—two college-age jazz DJs had interviewed Evans, and decided to document the concert using their radio station’s equipment. The recording, remastered from the original analog tapes, sounds all but pristine. Fusion was the fast-growing flavor of the day, but Evans continued to ply his elevated trade in a strictly acoustic format. As per his usual approach, he mixes original compositions with standards, starting with his own spritely “Sugar Plum,” which begins with two minutes of unaccompanied piano before opening up for a leapfrogging solo by Gomez. The leader’s “Time Remembered” is a nostalgia-laced mid-tempo piece, capped with Gomez’s arco improvisations. And the pianist’s aptly titled “T.T.T. (Twelve Tone Tune)” is more adventurous, with the three musicians dropping in and out of various sections in a kind of extended call and response. The set offers several familiar crowd-pleasers, including a freewheeling, time-tugging workout on Disney film waltz “Someday My Prince Will Come,” featuring some of the album’s most provocative soloing; a hard-swinging version of Cole Porter’s “All of You” and the somber, way-laidback closer “Some Other Time.” Two other tunes, Jerome Kern’s beautifully melodic “Up With the Lark” and the wistful, Brazilian-flavored “Minha (All Mine)” were relatively new to Evans’ repertoire. On a Monday Evening is a welcome and unexpected gem that illuminates the in-concert prowess of the Evans/Gomez/Zigmund lineup.