Heat the oil or lard in the casserole over a medium heat, add the chopped onion and fry until the edges become golden brown.
Add the beans to its broth, turn the heat up to bring it to a boil, then turn heat down to a gentle simmer. This step will take about 5 minutes. While the beans are warming up, start making the dumplings.
Place cornflour, pork cracklings, salt and warm water in a bowl and mix well. Gently knead the dough until it is very soft and smooth.
To form the dumplings divide the dough into 16 small balls, pressing your thumb in the center of each ball. This will form a little well, like a belly button in the center of the dumpling.
Add the dumplings to the simmer beans, the epazote branch (if using), and season with salt and keep simmering. Soup is ready as soon as dumplings float on the surface. Serve warm and enjoy!
If you don’t want to add the pork crackling to the dumplings, you can make them just with the plain masa corn dough. Other dumpling additions are chopped green onions, epazote, cilantro, and cheese.