R&R Tacqueria, 7894 Washington Blvd. (Rt.1); 410-799-0001, Elkridge, Maryland, 13 minutes north of the 495/95 intersection, look for the Shell sign.
This tacqueria is in a gas station, with two small counters and three chairs to sit on. It is the best huarache I have eaten, ever, including in Mexico. It is the best chile relleno I've had in the United States, ever. They serve among the best Mexican soups I have had, ever, and I have been to Mexico almost twenty times. I recommend the tacos al pastor as well. At first Yana and Natasha were skeptics ("Sometimes you exaggerate about food") but now they are converts and the takeaways have vanished. They even sell Mexican Coca-Cola and by the way the place is quite clean and nice, albeit cramped.
The highly intelligent proprietor is a former cargo pilot from Mexico City and speaks excellent English. The restaurant is called R&R after the names of his two sons.
For over twenty years I have sought such a place in the Washington, D.C. area and now I have one. For over twenty years people have been asking me how can they scratch this itch and now I have an answer. (The version of this post to appear on tylercowensethnicdiningguide.com will have photos of the food.)