These unusual enchiladas, with red chile ground in the masa, are sold from small stands in the industrial capital of San Luis Potosí. More like a quesadilla in appearance, they are usually served with shredded lettuce and guacamole.
Heat a comal or iron skillet over medium heat. Place the chiles in the hot skillet, using a spatula to press them against it lightly. Turn them so that both sides begin to change color. This will take about 1-2 minutes. Be careful not to burn them. Soak in the hot water for 25 minutes. Then purée chiles in a blender with 1/2 cup of the water in which they soaked. Melt the lard in a small skillet, add the chile purée and sauté for 5 minutes. Set aside.
Heat the oil in a small skillet, add the onion and sauté until transparent. Remove from the heat and stir in the cheese. Add 1 tablespoon of the chile purée and stir well. Set aside.
Place the masa in a bowl, add the remaining chile purée and the salt and knead until all the ingredients are thoroughly combined. Cover with a damp cloth and let rest for 20 minutes.
Form the masa into balls, place between 2 pieces of plastic in a tortilla press, flatten to form circles (about 3"). Remove the plastic. Spread the cheese mixture in the middle of each circle, leaving a narrow margin. Fold the circles in half and press the edges to seal.
Heat a comal or iron skillet and toast the enchiladas for 2 or 3 minutes on each side or until the masa changes color and seems cooked. Heat 1/2 inch (1 cm) oil in a skillet, add the enchiladas 2 or 3 at a time and fry for 3 or 4 minutes on each side. Drain.