Cast a Shakespearean in Sweeney Todd, and you might reasonably expect to discover fresh nuances in Stephen Sondheim’s blood-soaked revengical—little moments of performance clarity to go with the cannibalism and sumptuous melodies. And, in fact, discoveries do come fast and furious at Signature Theatre, though not in the role the classical actor’s inhabiting. As the throat-slashing demon barber of Fleet Street, Shakespeare Theatre stalwart Ed Gero’s doing a perfectly creditable, if vocally unremarkable job—eyes flashing with malice beneath a wig that makes him look like a demented Beethoven. But it’s his partner in crime—meat-pie-baking Mrs. Lovett—who’s the revelation here. Sherri L. Edelen nails guffaws on lines that never seemed like jokes before, dances little jigs and hitch-steps where most Lovetts waltz, and winks over her shoulder at the audience as she lies to the unwitting customers who’re wolfing down their neighbors about how careful she’s been with the coriander. Nor is she merely going for laughs. Look into this lovesick harridan’s eyes and you see how genuinely anguished she is at the realization she’ll have to kill the lad who’s just crooned that nothing’s gonna harm her, not while he’s around. Edelen has rethought Mrs. Lovett’s backstory and succeeded in making the role her own—no mean feat considering the dames who’ve wielded that rolling pin before her. And she’s not alone in doing some rethinking. Erin Driscoll’s Johanna may seem a conventionally ditzy ingénue, but she doesn’t hesitate to grab her boyfriend’s pistol and plug a pursuer when she’s on the run. Sam Ludwig’s vocally angelic Toby has shaved his head in such erratic patches you figure he must’ve had an encounter with some other mad barber on his way to the theater. And there are unusual grace notes to Chris Van Cleave’s full-voiced, malevolent Judge Turpin and Gregory Maheu’s wild-eyed Anthony. Elsewhere the cast is sketchier but not really in spots that matter, possibly because this is director Eric Schaeffer’s third Signature stab at Sweeney, and he can now manage it in his sleep. He went for intimacy the first time, tried nontraditional casting the second, and now that he has a theater with some headroom (and twice as many seats to fill), he’s making the Guignol grander with buckets of blood dripping from on high and bodies hurtling stageward from the rafters. Also rumbles thundering in the background for no better reason than that there’s a tympani in that orchestra perched in the scaffolding, and it would be wasteful not to make as much use of it as possible. Shattering this Sweeney is not, but it’s decently effective, and when Edelen’s shooting you a wink, a good deal more than that.