In a large bowl, stir together 6 tablespoons salted butter (room temperature), 3 tablespoons harissa paste, 2 tablespoons cider vinegar, 1 teaspoon grated orange zest and ¼ teaspoon each kosher salt and ground black pepper. Prepare, grill and husk the corn as directed. Add the husked ears a few at a time to the bowl with the butter mixture and turn to coat. Return the corn to the hot side of the grill and cook, uncovered and turning occasionally, until lightly charred on all sides, 5 to 7 minutes; move the ears to the cool side if flare-ups become too intense. Transfer to a platter, then sprinkle with the ⅓ cup lightly packed fresh mint (chopped).