1. Measure the masa harina and salt into a large bowl. Cut the butter into tablespoon-sized pieces and work it into the dry ingredients using the back of a wooden spoon. Add the water and mix with a wooden spoon or with your hands until a soft dough forms. Cover the dough with a clean cloth and let rest for 5 minutes.
2. Divide the dough into 12 pieces and roll each piece into a ball.
3. To keep the dough from sticking to the tortilla press, put a piece of plastic wrap (or a plastic bag) on the bottom surface of the press Put a ball of dough in the center of the plastic. Then place another piece of plastic wrap on the top of the dough. Press the dough flat in the press.
4. Pick up the tortilla with the plastic on both sides. Peel off one piece of plastic (which can be reused). Flip the tortilla off of the plastic onto a hot griddle. Cook for 1 to 2 minutes, until the bottom of the tortilla becomes golden. Flip the tortilla and press lightly with a spatula, which will make the tortilla puff slightly. Cook for one to two minutes more, until the tortilla appears to be done.