
Bring 2 cups of water to a boil in a small pot. Add the aji amarillo chilies and simmer for 10 minutes to soften. Drain and peel if desired.
Add the chilies to a blender or food processor with onion, garlic, salt, and oil. Process to form a chili paste. Add more oil or water while the processor is running to achieve a smoother paste, if desired.
Adjust for salt and pepper and serve!