Sharon Tyler Herbst says “these crumbly rich cookies are of Arab origin but they’re now popular in many versions throughout the world.” She goes on to say some recipes include lard, which I think precludes them being of Arab origin, or at least of Muslim Arab origin, but what do I know? And so I have turned to Wikipedia to deepen my knowledge a shallow bit. I am not sure that helps a whole lot, but polvorón and mantecado seem to be almost interchangeably translated to shortbread, and so I found the article interesting if not definitively informative.
Ms. Herbst prefers butter over lard or shortening in this recipe. She also provides two variations; one for Mexican wedding cookies with two cups of finely chopped toasted nuts added to the butter, powdered sugar, vanilla and flour, and the other for a chocolate version with cocoa, nuts and chocolate chips. I imagine both are delicious. I cheated and opted to shape these in balls rather than half-inch thick, two-inch long ovals. The latter looked a little too much like over-large suppositories for my taste, but I may have been shaping them incorrectly. The primary recipe calls for rolling the warm-from-the-oven cookies in sifted powdered sugar, letting them cool, and then rolling them in the powdered sugar again. The result is a melt-in-your-mouth sweet sensation as the whole confection crumbles into dust. Awesomesauce!