For this recipe, chef Rick Bayless uses a cast-iron or aluminum tortilla press to help flatten the tortillas.
To make the dough: If using fresh masa, knead the dough with a little cold water until soft and easily malleable. Add water, a tablespoon at a time, and stop when dough becomes soft, but not sticky. Cover with plastic wrap. If using masa harina, mix it with 1 cup plus 2 tablespoons hot water, then knead until smooth, adding more water or more masa harina to achieve a very soft (but not sticky) consistency. Cover with plastic wrap, and let rest for 30 minutes.
To press and unmold the tortillas: Divide the dough into 15 balls, and cover with plastic wrap.
Heat 2 ungreased large skillets or an ungreased double-size griddle (one that fits over two burners) so that one end is between medium low and medium and the other is at medium high.
Cut 2 squares of medium-to-heavy plastic (a garbage bag will work fine) to fit over the plates of the tortilla press. Place 1 square of plastic on the bottom plate. Center a ball of dough on the plastic, flattening it a little with your hand to make it stick, and cover with the other square of plastic. Close the top plate, fold the pressure handle over it, and press down somewhat firmly. Open, turn tortilla 180 degrees, close, and gently press again, to an even 1/16-inch thickness.
Fold back the pressure handle, open the top plate, and, while the plastic-wrapped tortilla is still lying on the bottom plate, take hold of the top piece of plastic, and quickly pull it off. Now, pick up the tortilla by the plastic with one hand, and flip it over, uncovered side down, onto the slightly separated fingers of your other hand -- it will cover your fingers and half of your palm.
Starting at one edge, quickly peel the remaining plastic off the tortilla, leaving the raw, flattened disc of masa on your hand. If the dough is too soft, you'll have difficulty peeling off the plastic; to correct the problem, work a little masa harina into the dough, and continue.
To cook the tortillas: Take a tortilla in your hand, and hold it at a 45-degree angle to the cooler skillet or cooler end of the griddle. Move your hand away from your body, letting the overhanging portion of the tortilla go down first, then quickly roll your hand out from underneath the tortilla, letting it fall flat and smooth.
The tortilla should begin to bubble after 15 seconds, at which point you should flip it onto the hotter surface.
Within 30 to 40 seconds, the tortilla should be speckled brown underneath. Remove from griddle, and use immediately.