Add oil to a cast-iron skillet, then add minced shallots. Sauté over medium heat until translucent. Mince garlic, add to pan, and sauté for another minute.
Pour two cans of black beans into the pan, including the liquid. Season with salt, black pepper, coriander, cumin powder, and Mexican oregano. Add lime juice and minced serrano (optional), then mix ingredients to combine. Simmer, uncovered, over low heat for 10-15 minutes.
Sprinkle with chopped cilantro and crumbled cotija cheese before serving.
Notes
Don't cook until all the sauce is gone. Go by the saucy consistency, rather than the cooking time.
If you prefer a smoother texture, you can mash the black beans with a potato masher to achieve the desired consistency.
You can also blend the bean mixture until smooth in a food processor to make bean dip, or to replace the bean layer in this Mexican refried bean dip.
Store leftovers in an airtight container in the fridge for up to 5 days.