In a city awash in pepper sauce, the dark dried chile salsa served at El Hidalguense on Long Point stands out as one of most intriguing. The secret to the richly flavored puree is the chile rayado of Hidalgo, one of Mexico's most interesting peppers. It has a fleshy dried chile flavor like an ancho, but with a chocolate-like bitterness and a subtle smokiness. The owner of El Hidalguense told me he gets a big batch of the dried peppers brought up from Hidalgo every two weeks.
Rayado means "rayed" in Spanish—a better translation might be "striped." In its green form, the chile rayado looks like a broad-shouldered jalapeño. As it ripens and turns red, it develops long striations—these are the "rays" that the name alludes to. The rays are most evident as the chile begins to dry.
The drying process is assisted by placing the chiles in a brick barbecue where they're stirred in deep pans over a wood fire until they turn dark brown. In the process, they acquire an aroma of woodsmoke that is pleasant without being as intense as a chipotle. Get over to El Hidaguense and see for yourself.
And here's a 10-minute video illustrating the chile rayado process: