Combine the butter with the lime zest, mint, chile powder, garlic, paprika and 1/2 teaspoon salt in a bowl until mixed evenly. Spoon the butter onto the long side of an 8-inch-square piece of plastic wrap, leaving a bit of space at the edge and on the ends. Cover with the extra plastic and roll up into a log, twisting the ends as you go. Refrigerate until ready to serve. Keep in the refrigerator for up to a week, or in the freezer for 2 months.
Pour the milk and 4 cups water into a Dutch oven and add the sugar, if desired. Bring to a simmer over medium-high heat.
Peel back the husks of the corn, keeping them attached, and remove all the silks. Close the husks around the corn. Place in the liquid and cook until the kernels are tender, 10 to 15 minutes depending on the freshness of the corn. Open the husks and top each corn with pat of the chile butter. Serve hot.