Coat the peppers with vegetable oil and place them on a sheet pan. Use a blowtorch to blacken the skin, turning the peppers to cook all sides. If you are making more than a single recipe, roast the peppers at 450°F (230°C) until blackened, turning them once or twice.
Wrap the peppers in a moist towel or place in a plastic bag; set aside to cool to room temperat