Add 1 tablespoon of oil to a medium skillet over medium heat, then fry the onion, garlic, and jalapeño until golden.
Add the black beans, bring to a simmer, and season with salt to taste.
Transfer everything from the skillet to a large blender and puree until completely smooth. Set aside.
In a large bowl, combine the masa harina and salt. Stir in the water until a dough forms. Using your hands, knead the dough until it fully comes together and all the water is absorbed, about 3 minutes.
Divide the dough into about 15 equal small portions, then roll each into a ball. Cover them with a clean damp cloth or plastic wrap to keep the dough moist while you work.
Heat a griddle or skillet over medium-high heat until hot.
Lay a piece of parchment paper on an open tortilla press and place 1 dough ball on the bottom half. Fold the other side of the parchment paper over the dough and gently close and press the upper portion of the tortilla press to flatten it out.
Open the tortilla press and carefully place 1 ½ tablespoons of black beans and 1 ½ tablespoons of shredded Oaxacan cheese to the center of the masa, spreading evenly.
Fold over the bottom side of the masa, then the top right corner and the top left corner to form a triangle. Gently press down each time you fold to seal the beans and cheese inside the dough.
Place the tetela on the hot skillet and cook for about 3 minutes on each side. Transfer it to a plate and cover it with a kitchen towel to keep it soft. Repeat this process until all the tetelas are cooked.
Enjoy immediately with your favorite salsa, crumbled queso fresco, Mexican crema, and fresh cilantro on top.
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Notes
Jalapeño: You can completely omit the jalapeño if you don't want any spice, or you can use a serrano pepper instead for more heat.
Beans: Canned black beans work great for this recipe’s filling, but you could also use homemade black beans. You would need about 1 ½ cups cooked black beans with ⅓ cup cooking liquid.
Cheese: Shredded Oaxaca cheese melts so well, but feel free to use Monterey Jack or Chihuahua if you prefer.