Carefully roast the chile peppers over the flame of your stovetop, on a grill or under the broiler. Using tongs, flip and move them around until their skins are completely charred. Transfer the chiles to a resealable plastic bag, seal the bag and let them steam for 10 minutes. Peel, seed and dice the chiles; set aside.
Preheat the oven to 375 degrees F.
Put the corn on a baking sheet, brush with vegetable oil and season with salt and pepper. Roast, turning halfway through, until cooked, 10 to 12 minutes.
Meanwhile, melt the butter in a small saucepan. Add the diced chiles, chili powder, lime zest and juice, 1 teaspoon salt and 1 teaspoon black pepper and stir. Cook on low for 2 to 3 minutes to allow the flavors to meld.
Transfer the corn to a serving platter (or a foil pan with a cover if transporting) and pour the chili butter over the corn. To serve, garnish with the chopped cilantro.