In a large bowl or large container, mix together the corn flour, water and salt, add it gradually until it reaches a uniform and soft textured dough. Pre-heat a pan and lightly grease it with oil. Lightly moisten your hands with some water to stop the dough sticking to your hands.
Take some of the dough and make a ball that resembles a large meatball, or slightly larger than a golf ball. Then flatten the ball lightly into a flat disk shape, resembling a patty or tortilla. Ideally you should keep the patty in one hand and hollow it inwards to create a concave, 'cup-like' shape. Add the cheese and the jalapeño slices to the centre of the patty, the amount of cheese you put in compared to the jalapeño slices depends on how hot you want it, but the portion should generally be slightly smaller than a golf ball in shape and size.
Close the patty into a dumpling-like shape, enclosing the cheese and jalapeños inside, then carefully flatten it back into a patty shape. Place the patty in the previously pre-heated pan on a medium temperature and allow it to cook for around three minutes on each side, flipping constantly with a spatula until the patty reaches a golden light tone. It is normal that dark spots appear on each side and melted cheese oozes out of the sides, this is a good indicator that the pupusa is now done.
You can enjoy the pupusa by itself or with the traditional curtido (pickled sliced cabbage or coleslaw) and salsa de tomate (fresh tomato sauce).
Recipe courtesy of Rafaol Soler