In a large bowl, stir together the masa harina and salt, then add the hot water. Knead the dough in the bowl until it has the consistency of Play-Doh. If the dough cracks when squeezed, it is too dry; add a tablespoon or two of water until you reach the right consistency. Cover with plastic wrap.
Heat a large cast-iron skillet over medium heat. Line a tortilla press with a plastic bag to prevent the dough from sticking. Line a plate with a kitchen towel.
Uncover the dough and pinch off 8 golf-ball-size chunks (about 1 3/4 ounces each). Roll them into balls and flatten them in the press to create 6-inch rounds.
Place one tortilla in the hot skillet. Cook for 30 seconds, flip with a spatula or tongs, cook another 30 seconds, and flip again. Cook until the tortilla slightly puffs up, about 30 seconds more. Transfer the tortilla to the towel-lined plate and cover with a paper towel. Repeat with the remaining tortillas.