Make the dough. In a large bowl, mix together the masa harina and salt. Add 1½ cups of warm water and stir until a dough starts to form. Use your hands to knead it together for about 3 minutes, until the dough is smooth and all the water is absorbed. It should feel soft and pliable, like Play-Doh, not crumbly or sticky. If it cracks when you press it, add more water a tablespoon at a time. If it sticks to your hands, add a little more masa harina.
Divide the dough into 12 equal balls. Place them on a plate or in a bowl and cover with a damp cloth or plastic wrap so they don't dry out while you work.
Set a comal or nonstick skillet over medium-high heat and let it get really hot. While it heats up, cut the seams off a large zip-top bag to make two pieces of plastic, or grab two sheets of parchment paper.
Press the tortillas. Lay one piece of plastic (or parchment) on the tortilla press. Place a dough ball in the center, add the second piece on top, then press. You're aiming for about 5-6 inches in diameter. Carefully peel back the plastic and transfer the tortilla to your hand.
Cook. Place the tortilla on the hot skillet. Cook for 15-20 seconds, flip and cook another 15-20 seconds, then flip one more time and cook for 30 seconds per side. This last flip is where the magic happens, and you'll see it start to puff up. Repeat with the remaining dough balls.
Keep warm. Stack the cooked tortillas in a tortilla warmer, or wrap them in a clean kitchen towel and tuck them into a zip-top bag. This keeps them soft and pliable until you're ready to eat.
Serve immediately or store tightly wrapped in the fridge for up to 5 days.
Notes
Storing and reheating: Let them cool, wrap them in a clean kitchen towel, and seal them in a bag in the fridge. Reheat on a hot skillet for 20 to 30 seconds a side, or right over a gas flame, and skip the microwave since it dries them out.
Adding fat: A small amount of lard or olive oil (about 1-2 teaspoons) can be kneaded into the dough to help keep the tortillas more pliable. Lard is the traditional choice, but olive oil works great too.
Thumbprint test: Take a piece of dough and roll it into a ball. Press down on the middle of the ball with a finger or the palm of your other hand. If the edges of the flattened ball crack, it's too dry and needs more water. It may feel like it doesn't need more water, but if it cracks, trust me - knead in a tablespoon or two of water at a time until it passes this test.
No tortilla press: If you don't have a tortilla press, you can use a large baking dish to flatten the dough in between two sheets of parchment paper. The trick is to press the dough as evenly as possible so that it's the same thickness all around.
Tortilla warmer: To keep the tortillas warm and pliable when serving, place them inside a tortilla warmer or wrap them in a clean kitchen towel and place them inside a large resealable storage bag to help them retain heat and moisture.