There’s a certain voyeuristic delight in discovering a performer who, poised for national or even international renown, is still largely a local secret. That’s how I felt a decade ago upon hearing Patricia Barber’s first CD, purchased from Barber herself after one of her Chicago club dates. Rebecca Parris evokes the same thrill, and savvy Bostonians have long had the privilege of celebrating her vocal prowess. Parris sings grown-up songs for grown-ups with a gutsiness that only a providential blend of talent and maturity can produce. So consistently good is her current collection of ballads, My Foolish Heart (Koch CD-7887; 61:07), that it is not only unfair but well-nigh impossible to single out any of these languid, smoky tracks for individual praise. Parris treats “The Shadow of Your Smile” and “Yesterday I Heard the Rain,” two achingly beautiful laments to loss and loneliness that have been handled far too lightly far too often, with the same reverence as “Lover Man,” “Body and Soul” and “Crazy He Calls Me.” Like a perfectly matched set of nine fiery diamonds, My Foolish Heart is the kind of accomplishment that should make the much too secret Parris a secret no more.