If pert Sarah Partridge seems vaguely familiar, chances are you spotted her alongside Tom Cruise in Risky Business or swapping lines with the likes of Helen Hunt, Angela Lansbury and Heather Locklear in guest spots on Mad About You, Murder, She Wrote and Melrose Place. But that’s all behind her now. One fateful Sunset Strip night in the early ’90s, Partridge reluctantly let her party pals talk her into a performing a karaoke rendition of “Summertime.” In one of those only-happens-in-Hollywood scenarios, an L.A. booker happened to be within earshot, liked what he heard and ultimately convinced her to swap occasional film and TV roles for a fulltime singing career. Since then she’s crisscrossed the country several times, winning warm reviews for her club dates on both coasts, and set down an impressive debut disc (1999’s I’ll Be Easy to Find which, believe me, ain’t that easy to find). On her sophomore outing, Blame It On My Youth (Nagel-Heyer), Partridge favors an invitingly pleasant approach that tends to be as sunny as her blonde locks. For the most part, such effervescent purity serves her well, especially on carefree numbers like “Cheek to Cheek,” “I’ve Got the World On a String” and a puckish “How Long Has This Been Going On” that positively bubbles with joie de vivre. Conversely, her oddly buoyant “Every Day I Have the Blues” seems inappropriately happy, her “Haunted Heart” seems lacking in genuine heartbreak and her “Blame It on My Youth,” though lovely, isn’t quite bruised enough. Still, her ability to capture precisely the right sense of world-weary sophistication on “Just One of Those Things” and to underscore the unconditional loyalty of “Come Rain or Come Shine” with a canny note of caution indicate that Partridge has the potential to mature into a fine pop-jazz chanteuse.