Cheese enchiladas are some of my favorite old school Tex-Mex food. Corn tortillas, orange cheese, smothered in a beefy thick gravy. The gravy is not like a typical Mexican enchilada sauce: no tomatoes or tomatillos. Instead it’s more of a Southern gravy like you’d put on biscuits or serve with turkey, but spiced with chile, cumin, oregano, and garlic powder. The key thing is it’s made with a roux. And a lot of roux, it really is a thick gravy. You never see this sauce in California or New Mexico and I suspect not in Mexico itself except maybe at the border. But it’s everywhere in Texas. it’s a defining element of Tex-Mex cuisine.

There’s an early recipe for the Tex-Mex gravy in the 1908 Gebhardt Chili Powder Company cookbook. This cookbook was written for Americans for whom Mexican food was exotic. It was written mostly to sell their chili powder, a spice blend of mild chiles (probably ancho), cumin, oregano, and garlic powder. (I made a PDF of the book from these scans.)

Salsa de Chili—Chili Gravy
This may be made of any brown or meat gravy by adding to each one-half pint of gravy, one teaspoonful of Gebhardt Eagle Chili Powder, stirring thoroughly and cooking for ten minutes. This makes a very rich sauce for fried eggs, cooked rice, baked beans, etc.

Note it doesn’t mention enchiladas. There’s no enchilada recipe in the copy of the book I have. But this is our Tex-Mex gravy! Although it’s awfully light on the spice.

Robb Walsh’s Tex-Mex Cooking has a modern version of the same gravy, see the NYT version. It’s a 4:1 mixture of chicken broth to roux with Tex-Mex spices added. Walsh’s recipe says

The lifeblood of old-fashioned Tex-Mex, chili gravy is a cross between Anglo-brown gravy and Mexican chile sauce. It was invented in Anglo-owned Mexican restaurants like The Original.