Toast the chiles in a hot, dry skillet for about 30 seconds per side. Allow chiles to cool and then remove stems, and shake out as many of the seeds as you can.
In the same hot, dry skillet char the onion, tomatoes and garlic.
Place the chiles back in skillet with the charred onion, tomatoes, garlic and add the Mexican oregano, marjoram and salt. Add enough water to cover and bring to a boil. Lower heat and simmer for 10 minutes.
Carefully remove boiled chiles, vegetables, herbs and the water and put in a blender. Purée until smooth. If too thick, add a little water to blend completely.
Strain chile vegetable mixture through a sieve into a bowl and be sure to scrape bottom of sieve to get all the pulp.
Heat the skillet over medium high heat and add the oil. Quickly and carefully add the strained sauce to fry it. Reduce the heat and simmer for 20 minutes until the sauce has thickened stirring often.
Add salt and or sugar to taste.
Cool completely, cover and store in an airtight container in the refrigerator for up to 2 weeks.
Video
Notes
I like to add Roma tomatoes, although this is not traditional. Cut these lengthwise if using.
Nutritional information shown is for 1 cup of enchilada sauce. The recipe yields 4 cups total, enough for approximately 8 people.