Combine sauce ingredients in saucepot. Taste. Adjust seasoning if necessary.
Blanch asparagus in lightly salted water. Slice tuna and season with salt and pepper. Roll asparagus with tuna slices and briefly saute in hot oil. Strain the sauce through a chinois. Reserve the shiitakes. Thinly slice the shiitakes, combine with the reserved asparagus tops, and finish the sauce with butter. Add the sauce to the pan and reduce by one third.
Place sauce on plate with asparagus and shiitake mixture in center and tuna on top.
Recipe courtesy of Aspen Culinary Cooking School, Colorado