Preparation

1. Heat the lard in a skillet over medium heat. When hot, add the onion wedge and garlic. Fry, turning occasionally, until blistered and deep golden brown.
2. Add the beans and mash roughly, using the bottom of a heatproof cup. You don’t want them too pasty and smooth. In Spanish, they call the desired texture martajada. Add a little bean broth if they look too dry. Cook until the flavors combine, adding more broth as needed, about 5 minutes. Season with salt. Transfer to a bowl nearby.
3. If you’re using masa harina, place in a deep bowl and pour 1 cup of the warm water on top. Knead together for about 5 minutes to form a thick, pliable dough. To check whether the dough is sufficiently moist, break off a small ball and flatten it. If the edges crack, you need more water—up to 1/2 cup. (The masa should be moister than the average tortilla masa, as it will cook longer than a tortilla and shouldn’t dry out.) If using fresh tortilla masa, sprinkle with a few drops of water and knead firmly, adding the water a teaspoon at a time until the masa is very soft and creamy, about 5 minutes. (For fresh masa you will only need perhaps 1/4 cup water total.) Grab a piece of masa and cover the rest with a damp dish cloth to keep it hydrated.
4. Roll the masa into a ball just larger than a golf ball, and using your palm, flatten into a disk about 1/4 inch thick. (You can also place the ball on a tortilla press, but be careful not to press it too thin.) Fresh masa will be much easier to work with than masa harina, but if you’re using the latter, keep working and patting, pressing firmly on the masa ball to form a circular shape.
5. Holding the disk in your palm, add 1 to 2 tablespoons beans or requesón to the center, spreading the filling into a longish rectangle, without hitting the top or bottom edges. The filling amount really depends on how big your disk is—if the filling spills out when you try to close the tlacoyo, you have too much.
6. Fold both sides of the tlacoyo toward the center to enclose the filling. Press the seams together, pinching them closed with your thumbs. Pinch the seams closed with your thumbs. Set aside on a baking sheet and repeat with the remaining masa and filling.
7. Warm a comal or nonstick skillet on medium heat. Place the tlacoyo in the pan, without oil, and let cook. Once the sides start to dry slightly, turn it over. If you don’t start to see golden brown freckles, turn up the heat; if you see burned spots, lower the heat. Keep turning at intervals until both sides are freckled and crisp, and the edges have puffed a bit, 10 to 12 minutes in all.