For the chicharron: Place the whole pork in pot with 1/2 cup water to cover the bottom of the pot. Simmer until tender, about 1 hour. The water will have absorbed or evaporated. Pan fry the pork for 2 to 3 minutes in the dry pot. Place the meat in a food processor and grind with the onions, peppers and tomatoes until it produces about 1 cup of paste.
For the pupusa dough: In a large bowl, stir together the masa harina with the water and salt if using and mix it well. Add more water if the dough becomes too hard or cracked. Let the dough rest, covered with plastic wrap, for about 15 minutes.
While the dough sits, make the filling: Mix the refried beans, if using, in a food processor until smooth. Then mix together with the cheese and 1 cup chicharron.
Divide the dough into about 6 pieces. Form a ball of dough, and then make a pocket in the ball. Place a tablespoon of your filling in the pocket, and carefully wrap the dough around the filling to seal it inside the dough ball. Flatten the ball into a flat disk shape about 1/4-inch thick. Make sure the filling does not leak.
Coat a very heavy skillet, such as cast iron, with a small amount of oil. Heat the skillet over medium heat, and place the pupusas in the skillet. Allow to brown on each side, flipping as necessary, 5 to 6 minutes. Remove from the heat and serve warm.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.