In a medium bowl, whisk together the masa harina and the salt. Add the lard and the hot water and use a spoon to mix, pressing the spoon into the dough and moistening all dry spots. Using your hands, mix and knead the dough further to develop the gluten, about 1-2 minutes more. The dough will be very wet. Cover the dough and allow to rest at room temperature 1 hour. (During this time, the masa harina will continue to soak up the moisture from the water, creating a tender-- but not sticky-- dough.)
After 1 hour, uncover the dough. Test the dough by taking a tablespoon of the dough and forming a ball. Press the ball between your palms. If the edges crack more than 1/4 “, the dough is too dry. If it sticks to your hands, it’s too wet. If needed, knead in any additions of masa or hot water into the dough, cover, and rest 10 minutes. If the dough doesn't crack or stick badly, you’re ready to make tortillas!
Turn the dough out of the bowl onto a clean surface and knead a few times. Divide the dough evenly into 16 pieces, then roll each piece into a ball. Place the balls back into the bowl and do not cover.
Cut the zipper top and side seams off a gallon zip top bag. If you’re using a tortilla press, place this liner inside your press. If you’re using a DIY press (see video above the recipe), place this liner on your work surface. Place one ball of dough between the two pieces of plastic, then flatten into a tortilla with your press or pan.
Heat a non-stick griddle or large non-stick pan over medium heat. When hot, use the plastic zip bag liner to lift the tortilla and gently transfer to your palm. Drop/smack the tortilla onto the hot griddle or pan by flipping your palm downward. Count to 15, then use a spatula to carefully flip, guiding the tortilla with your fingers. (At this stage, the tortilla will be delicate and prone to folding on itself.) Count to 25, then flip again. Count to 25 again and this time the tortilla should begin to puff. Flip for the last time and count to 25. (There are 4 turns total, with the tortilla puffing on the 3rd and 4th turns.) Transfer the tortilla to a basket or pan lined with a lint-free towel, and cover 3/4 of the way. (This post-cook steam is the final step of the process, don't skip it! The tortillas must steam well all the way through to be soft and pliable.) Continue pressing, cooking, and steaming the tortillas until all have been cooked.
Notes for cooking: If the tortilla is getting black spots after the second turn, the heat should be decreased. If the tortilla isn’t puffing on the third turn, the heat should be increased.
Leftover tortillas can be stored in an airtight container in the fridge, but must be reheated all the way through to be pliable and soft again. To reheat, wrap in a towel and steam in a steaming insert or bamboo steamer.