Make the Sesame Soy Butter Baste: Melt the butter in a saucepan over medium heat. Add the sesame seeds, garlic, and scallions and cook until the garlic and scallions are aromatic but not brown, 3 minutes. Stir in the soy sauce and pepper. Simmer for 2 minutes. This is so quick and easy to prepare, there’s no reason not to make it right before using. However, you can make it in advance. If storing, transfer to a jar, cover, cool to room temperature, and refrigerate. The baste will keep for at least 1 week. Reheat to melt the butter before using.
Make the corn: Set up your grill for direct grilling and preheat to high. Husk the corn, stripping the husks back as though you were peeling a banana, leaving them attached at the base. Tie the husks back below the corn to make a handle, using a strip of husk or a string. (Alternatively, strip off the husks altogether and impale the grilled corn on wooden skewers.)
Lightly brush the ears of corn with the butter baste. Grill the corn until nicely browned on all sides, 2 to 3 minutes per side, 8 to 12 minutes in all, rotating the ears so they grill evenly. Position the corn so that the tied husks hang over the edge of the grill or away from the hot coals, or slide a folded sheet of aluminum foil under them so they won’t burn. Continue to baste the corn on all sides with the butter as it grills.
Transfer the corn to a platter. Sprinkle with the black sesame seeds and serve.