4 cups masa harina (corn flour, Quaker and Maseca brands are the best)
1/2 tsp salt
2 1/2 cups hot but not boiling water
Place the masa harina and salt in a large bowl. Add the water and mix with your hands to make a dough that comes together in a soft ball. Continue mixing and kneading until the dough is elastic enough to hold together without cracking, about 3 minutes. If using right away, divide the dough into 18 equal portions and cover with plastic wrap or a damp towel. If making ahead for later use, wrap the whole ball in plastic wrap and refrigerate for up to 1 day and then divide.
To form the tortillas, place a portion of dough between 2 pieces of plastic wrap. Press with a tortilla press or roll out with a rolling pin into a circle 6-7" in diameter. Use your fingers to smooth any raggedy edges. Continue with the remaining portions until the dough is used up.
To cook tortillas, heat a heavy skillet or griddle over high heat until it begins to smoke. Peel the plastic wrap off the tortilla and place the tortilla in the pan. Reduce the heat to medium-high and cook for 30 seconds. Turn and cook on the other side for 1 minute. Turn again, and cook until the corn tortilla puffs a bit but is still pliable, not crisp, about 30 seconds more. Remove and continue until all the corn tortillas are cooked. Store in container with lid until ready to serve.