Este sitio tiene una receta para pupusas. This recipe claims to be pura Salvadorena though they classify them as "Cheese, Chicharron, or Mixta" while on my trip everyone called them either "Cheese, Chicharron, or Revuelta". It's basically the same thing, but slightly different.

Anyway - it looks like a very good recipe to me. Now I just need to try it out.

Preparing the dough

There are different brands of tortilla flour to make the dough. MASECA, which can be found in most large supermarkets in the international section, is one of them but there are others. Follow the instructions on the bag and make as much dough as needed. Once the dough has been prepared set it aside while you prepare the filling.

Three Fillings

CHEESE

3 cups of shredded cheese (use hard and cream cheese mixed together; you can mix frying cheese, mozzarella and ricotta)

3 or 4 tablespoons of heavy cream

1/2 to 1 cup of ground "oroco" (this will be hard to find in the U.S. So you can use very finely chopped green peppers or scallions instead)

Salt to taste

Make a paste with these ingredients. To avoid the paste leaking, it should not be too soft.

"CHICHARRON"

1 cup cooked bacon (cooked with garlic, see below).

4 - 5 tomatoes

Salt to taste.

Cook bacon with some garlic (optional). Set fat aside but do not discard. Once cooked, grind bacon with the tomatoes, 1 green pepper, and salt to taste. Mix with some of the bacon fat until it has a soft consistency

MIXTAS

Ground and fried beans (they can be canned or prepared from your favorite recipe).

When filling the pupusas add beans, chicharron and cheese (or combine two of the three).

Making the pupusas

With two tablespoons of dough make a ball using your hands and later clap your hands until you make a round, thin (1/8 of an inch thick) tortilla. Continue making more tortillas this way. Put filling over one tortilla, cover with another and push down the sides to close them. This is the "beginners" method.

People who have experience do it this way: make a ball with the dough. Insert your thumb in the ball and make a hole in the center. Fill that hole with the filling, close the hole by pushing the dough on the sides up. Clap your hands carefully so that the filling doesn't come out and flatten the ball.

Cook on a slightly greased griddle, pan or electric pancake griddler and cook over low-medium heat (325-350 F) first one side, then the other until they are cooked. Each side will be ready when it no longer sticks to the pan (depending on the thickness of the tortillas, this might take 4 minutes or more per side).