Mix masa flour, salt, optional butter (if using), and water in a large mixing bowl. Stir until it comes together into a ball of soft and pliable dough. You can add more flour or water as needed.
Mix the beans and chilies in a small bowl.
Scoop ¼ cup of dough and flatten into a round 4- – 5-inch tortilla disc. I did this between pieces of parchment paper to prevent the dough from sticking. This can also be done by tortilla press or tortilla roller.
Spoon 1 – 2 T. bean/chilies mix in the center of the dough. Top bean mix with 1 – 2 T. cheese.
Fold the edges of the dough up and over the bean/cheese filling. Pinch the dough edges together and pat down into a flat disc again.
Heat a large, lightly oiled skillet over medium heat. Cook the pupusas about 4 – 5 minutes each side. They should be firm and crisp.
Serve immediately with sides of salsa and hot sauce.
