Bring a pot of well-salted water to a boil and set up an ice bath (a large bowl filled with water and lots of ice).
For nori butter: Melt the butter in a small skillet. Crumple and tear the nori sheet into pieces and infuse over very low heat for five minutes. Remove from heat and let stand for 15 minutes, then strain through a fine-mesh strainer. The nori butter can be stored overnight in the refrigerator.
For lemon garnish: Juice the lemon half and reserve the juice. Cut the juiced lemon shell in half again, squish the pieces flat on your cutting board, and carefully remove all of the membranes and white pith, leaving only yellow skin. Trim the sides to make two even rectangles.
Blanch the lemon skins in the boiling water for 30 seconds, remove them with a slotted spoon, then shock them in the ice bath and drain on paper towels (leave the water boiling on the stove). Cut first into 1/16-inch strips (fine julienne) and then into 1/16-inch squares (brunoise). The lemon garnish can be stored overnight in the refrigerator.
For asparagus: Trim asparagus to uniform length and use a paring knife to remove all the leaves. Blanch asparagus until crisp-tender and bright green, about three minutes. The tip of a knife should go in easily, but the stalks should offer a hint of resistance. Drain asparagus, shock them in the ice water, drain again, and reserve. The asparagus can be stored overnight in the refrigerator, wrapped in plastic.
For sauce: Whisk together the miso, mirin, and reserved lemon juice. Aim for a consistency that allows you to make a dot of sauce that will stand up on a plate, adjusting the liquid a bit to make it thicker or thinner. Put the sauce in a squeeze bottle. The miso-lemon sauce can be stored overnight in the refrigerator.
To clean green asparagus from insects, the tips as well as the triangular side leaves should be cut off and discarded. Alternatively, use frozen, thawed asparagus with a reliable hechsher.
When you are ready to serve, have four warmed plates waiting, and preheat the oven or toaster oven to 500 degrees Fahrenheit. Heat the nori butter in a saucepan. Bring the miso sauce back to room temperature, if necessary.
Brush asparagus with the nori butter. Spread asparagus on a baking sheet and reheat them in the oven (this should just take about three minutes).
Arrange six asparagus spears in a neat row on a dinner plate. Drizzle on more of the nori butter. Add neat lines of nori strips and sesame seeds. Make six large dots of the miso sauce and top each one with a chive tip. Randomly place bits of blanched lemon zest on the plate. Repeat for the remaining three servings. Sprinkle liberally with salt and serve.