Some recipes call for cilantro leaves only, but I threw in the stems as well to add some liquid to the sauce. I know cilantro is an acquired taste, so substitute with iceberg or romaine lettuce if you want a neutral taste but want to retain the green color.
Halve and de-seed the chili peppers. Make sure you wear gloves or thoroughly wash your hands afterward. And don't rub your eyes!
Puree all the ingredients in a blender, food processor, or hand immersion blender. It's like making pesto, start with the basic portions and adjust according to your taste. What worked for me was roughly those amounts. Add mayonnaise for creaminess. You can add water too if the sauce appears too thick. I've seen some recipes that called for white cheese or nuts, but felt those were too strong in taste since the versions of aji sauce that I've liked were light in flavor, with just an undertone of spiciness.