Step 1

Sauté the onion in a non-stick saucepan until softened and add garlic. Cook for one minute more. Add the remaining filling ingredients, except the lime juice, and cook for about 5 minutes, until hot. Using a potato masher, mash the beans until they are creamy. Simmer uncovered, stirring often, until most of the liquid is absorbed, about 5 minutes. Remove from heat and stir in the lime juice. Set aside to cool as you make the dough.

Step 2

Put the masa harina into a large bowl or into the bowl of a stand mixer. Add 3 cups of water and stir. Add more water until the mixture clings together and forms a dough. It should be soft and pliable and not crack when you press on it. Knead the dough for about 2 minutes (1 in a mixer fitted with a dough hook).

Step 3

Divide the dough in half and return half to the mixing bowl, covering it with plastic wrap. (If you like, you can refrigerate half the dough to use later, as I did.) Take the other half of the dough and divide it into 9 equal pieces. Cover 8 of the pieces with plastic wrap or a damp cloth while you work on one piece.

Step 4

Form the piece of dough into a ball, and place it in the palm of your hand. Use your fingers to make a hole in the dough and work it until you form a cup that has walls that are about 1/4-inch thick.

Step 5

Add about 1 to 1 1/2 tablespoons of beans to the “bowl,” enough to cover the bottom but leave at least 1/2-inch clean at the top.

Step 6

Pinch the sides together, leaving a little extra “nub” at the top.

Step 7

Pinch off the little nub of dough, sealing the top, and return the piece of dough to the bowl (you can gather all the pieces at the end to make another pupusa).

Step 8

Now’s the tricky part. Gently but firmly press on the dough to flatten it out. Try putting it in your left hand and pressing down on it with your right as your right thumb also compresses it from the side. When it’s flat, put it down on a cutting board and use your hands to flatten it even more, until it’s between 1/4 and 1/2-inch thick and about 4-5 inches in diameter. Take care not to squeeze the filling out, and repair any small tears by pinching them closed (or even take a bit of dough to make larger repairs.)

Step 9

You can make all the pupusas this way and then heat your griddle and cook them all, or you may cook each one as you make it. (I prefer to make a couple, get them started on the stove, and continue shaping pupusas as the first two cook–it seems to be quicker this way.)

Step 10

Heat a cast iron griddle or skillet over medium-high heat. Cook the pupusas until brown spots appear on the bottom and the tortilla appears dry, about 3-4 minutes. Then turn over and cook until the other side is browned. Keep them warm in the oven until all of them are cooked. Serve hot.