With a microwave: Dribble 3 tablespoons of water over a clean kitchen towel, then wrap your cold tortillas in it (you can also use damp paper towels). Slide the package into a microwaveable plastic bag and fold the top over-don't seal it. Microwave at 50% power for 4 minutes to create a steamy environment around the tortillas. Let stand for 2 to 3 minutes before serving.
With a vegetable steamer: Set up a vegetable steamer (one without that little post sticking up). Pour about 1/2 inch of water into the bottom. Wrap the cold tortillas-no more than 12 at a time-in a clean kitchen towel. Lay the package in a steamer, set the lid in place and set the pot over high heat. When steam comes puffing out, set the timer for 1 minute. Then turn off the heat and let the tortillas sit in their steamy world for 10 minutes. They're ready.