Dry toast chiles by slowly running them over the flame on a stove. If you have an electric stove, heat a skillet on medium heat, place the chiles in a skillet, and toast each side for about 30 seconds or until the chiles are soft and flexible.
Cut a slit in the side of the chiles, open the chiles, and remove seeds and stem.
Place chiles in a small pot, cover with 2 cups of water, and bring to a boil. Turn off the heat, cover the pot, and let the chiles soften in the water for 30 minutes.
Heat 2 teaspoons of avocado oil in a medium-sized saucepan. Add onions, 1/4 teaspoon salt, and 1/8 teaspoon pepper. Cook until the onions are beginning to caramelize.
Place chiles, chile cooking liquid, boullion, and onion mixture in a blender and puree. Push the mixture through a sieve.
Heat 2 Tablespoons avocado oil in a saucepan over medium heat. Add flour and mix for a minute to form a paste.
Slowly whisk in the chile mixture. Bring to a boil, then reduce heat and simmer for five minutes.
Taste and adjust seasoning if needed.