Heat coals in a grill. Once they are too hot to keep your hand directly over them for 2 seconds, add onion, garlic, tomato, and chile pods. Move them occasionally with tongs to char the sides evenly. Once chile pods begin to blacken on both sides, remove and place into 1–2 cups of recently boiled water. Let sit for at least 15 minutes (soaking the pods makes them easier to break down into a paste).

Meanwhile, once garlic is soft and roasted through, remove and set aside until cool enough to peel. When onions are charred on each side, remove and set aside. Once tomato is charred on each side and is soft throughout, remove carefully and set aside.

Peel garlic and, along with a couple pinches of salt, place in the molcajete. Grind it into a paste with the tejolote (pestle). Once it is a smooth paste that coats the bottom of the vessel, add the onion and grind until it also is smooth. Add soaked chile pods (do not add any of the chile water), and grind into garlic-onion paste until smooth.

Add tomato, and begin to mash it gently, taking care not to splash the tomato juice.

As it becomes more liquified, grind it into the base of the vessel until the salsa has a smooth consistency.

Add salt, to taste.