Make your masa dough. Mix the masa harina with the hot water and knead into a cohesive dough, about 2 or 3 minutes. You may need slightly more or less water: What you want is a moist masa that does not stick to your hands.
Cut out two sheets of plastic from a supermarket produce bag; the flimsy ones. These are better than heavy plastic. Put one sheet on your tortilla press, then pull off about 40 grams of masa dough, a bit larger than a walnut, or exactly the size of a walnut in its husk. Roll it into a ball and set it on the plastic. Put the other piece of plastic over it and press down with your hand a bit to flatten the dough somewhat. Lever your tortilla press down hard, but not all the way. Flip the tortilla over and lever it down again. This makes an evenly flat tortilla.
Get a large frying pan or heavy pot and pour enough oil to come up at least 1 inch up the sides, and ideally 2 inches. Heat it to between 325°F and 350°F.
Peel off the top piece of plastic and spoon a heaping tablespoon, more or less, onto the side of the dough closest to the lever, leaving about 1/2 inch space from the edge of the dough.
Gently fold the other side of the dough over the filling to form a half-moon. Carefully peel the plastic back and gently pat down the filling and seal the edges. Anchor the seal with the tines of a fork. Keep in mind the empanada is still sitting on the plastic.
Carefully lift the empanada off the plastic and slip it into the hot oil. It do this flat side down to start, then flip the empanada after about 2 minutes, letting the top fry about 90 seconds. Flip once more for another minute of frying, for a total frying time of about 4 to 5 minutes.
Make another empanada while you are frying the last one; usually you can have 2 or 3 frying at once. Lift the finished empanadas out and let them drain on a rack. Eat hot.