We use mild cascabel chiles for our chile oil, which give it a pleasantly toasty, smoky flavor. Cascabel chiles are easy to find in the Yucatán. We buy them by the shopping bag. In the United States, look for them in a Mexican market or online. - Excerpted from Hartwood by Eric Werner and Mya Henry with Christine Mulke and Oliver Strand (Artisan Books). —Food52
Combine the chilies, onion, and herbs in a deep, sturdy 10-inch pan. Pour in enough olive oil to cover. Cover the pan with aluminum foil and roast for 1 1/2 hours. Let cool.
Strain the oil into a 1-liter measuring cup; discard the solids. Return the oil to its original bottle (simply pour through a funnel set into the neck of the bottle). Cover and keep in a cool, dry place (it will last longer in the fridge, just remember to take it out about an hour before cooking to liquefy).