Step 1: Prepare the corn: Strip back the husk, starting at the top of the ear of corn. The motion is like peeling a banana. Leave the husk attached at the stem end. Remove all the corn silk, then fold the husk back and over the stem to form a handle. Tie with butcher’s string.
Step 2: Make the sesame-soy butter: Melt the butter in a saucepan over medium heat. Add the scallions and white sesame seeds and cook until sizzling and fragrant, 3 minutes. Remove the pan from the heat and stir in the tamari.
Step 3: Set up the grill for direct grilling and preheat to high. Arrange the corn on the grate with the foil grill shield under the husks. Grill until the kernels are handsomely browned, 8 to 12 minutes, turning periodically so the corn browns evenly. Baste the corn with the sesame soy butter as it cooks.
Step 4: Transfer the corn to a platter and brush with the remaining butter. Sprinkle with black sesame seeds and serve at once.