In a medium bowl, combine the masa, salt, and fat of your choice. Stir with a fork to mix evenly. Slowly pour in the hot water while continuing to stir, until a dough forms. (You want the dough to be damp and slightly tacky, because the masa will absorb some additional water while it rests. I usually use about 1 cup plus 3 tablespoons.) 

Knead the dough briefly with your hands until it forms a smooth ball. Wrap tightly in plastic wrap and let it rest at room temperature for at least 30 minutes or up to a few hours. 

When ready to cook the tortillas, set a cast iron skillet to warm over medium-high heat, and divide the dough into 10-12 roughly equal pieces. (If I’m feeling particular, I use a kitchen scale to make sure the pieces are about the same size. If it’s already late and my toddler is “helping,” eyeballing is just fine. :) Roll each piece into a ball. Working one at a time, place balls between two small cut-out pieces of a plastic grocery bag, then flatten each using a tortilla press, two pie plates or pans pressed together, or a rolling pin. 

As each tortilla is shaped, peel from the plastic and transfer to the warm skillet. Cook about 1 minute on each side, just until it begins to char and develop small bubbles. Wrap cooked tortillas in a clean kitchen towel, which will help them stay soft until ready to serve. Use immediately, or store tightly wrapped in the fridge for 3-4 days.