Place the peppers on a baking sheet and roast in an oven that’s been preheated to 400°F.—alternatively, put the peppers on the grates of a hot grill. Turn the peppers occasionally during roasting to char on all sides. This can take 20 to 30 mins.
The key to the peppers’ intense flavor is high heat—you want them to char a little during roasting.
Remove the peppers from the oven or grill when they’ve softened and are charred in places. Put them into a plastic grocery bag and let them stand for at least 10 min. Steaming them in the bag helps loosen the charred skin from the flesh.
Peel off the charred bits of skin with your fingers—you may be be tempted to rinse the peppers as you peel, but don’t. It will just wash off the flavorful oils. Separate the flesh from the seed core, cut as desired and store the peppers in resealable plastic bags or containers.
Refrigerate roasted peppers for up to 1 week or freeze for up to 1 month.