Cover the pork well with water, add the onion and salt, cover, and cook over medium heat for about 20 minutes. Add the cbilacayote and cook until both are tender-about 20 minutes more. Drain and reserve the broth.

Toast the chiles lightly on both sides, cover with hot water, and leave to soak for about 15 minutes.

Put 1 cup (250 ml) of the reserved meat broth into a blender. In a dry skillet, toast first the chile seeds until they turn a deep golden color, then the pumpkin seeds until they swell and begin to pop about, and last the sesame seeds until they turn a pale golden color. Transfer to the blender and blend to a textured puree, adding a little more of the broth if necessary.

Strain the chiles and transfer to the blender jar with 1 more cup (250 ml) of the broth and blend all together to a thick-textured consistency. Pour the mixture into the pan with the meat and chilacayote and the rest of the broth and continue cooking over low heat for about 10 minutes. Adjust salt, add the epazote, and cook for 5 more minutes.