Button Shiitake and Asparagus Stir-Fry

If you are lucky enough to locate hard-to-find little button shiitake, showcase them in a simple dish. The handsome dark caps, tender enough to be cooked with their pale stems intact, contrast sleekly with crisp, grassy asparagus. Powdered sansho, the Japanese name for a type of prickly ash, is not strictly necessary, but it adds an intriguing whiff of lemon, mint, pine—je ne sais quoi.