I've always felt that the tortillas for a taco—just like the crust on a pizza or the bread for a sandwich—are at least as important as what goes inside it. This makes it particularly distressing to see the number of taquerias that simply don't heat their tortillas correctly.
Making great tacos doesn't require you to make your own tortillas (though you can, if you so desire)—just like many sandwich shops get their bread from great bakeries, many great taquerias use tortillas made in local tortilla factories. You do, however, have to know how to heat them right.
The ideal tortilla should be soft, supple and moist with a bare hint of flakiness and some nice brown/charred spots on its surface.
How do you accomplish this? Well, first off, as tortillas get old their starches recrystallized, turning them stale. You combat this by heating them in a moist environment. You could set up a steamer, but much faster is to simply dip the tortilla in water and toss it straight on a hot surface. As the surface moisture evaporates, it steams the tortilla until it's soft all the way through. Meanwhile, the hot contact with the pan gives it some nice toasty browned spots.
Finally, stacking the heated tortillas and wrapping them in a towel is an essential final step, allowing them to soften with their own steam until they are perfectly tender.
Watch the video for full instructions.
Another Important 2-Minute Video
How To Make Mayonnaise (in 2 minutes or less) »
About the author: J. Kenji Lopez-Alt is the Managing Editor of Serious Eats where he likes to explore the science of home cooking in his weekly column The Food Lab. You can follow him at @thefoodlab on Twitter, or at The Food Lab on Facebook.