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