Heat a pan over high heat. Add the half-onion (unchopped), garlic cloves, and tomatillos and char well.
Once the surfaces of the vegetables have been well-charred, remove to a blender along with the cilantro and puree.
Heat lard in pan over medium heat. Add chicharrones and allow to sautee for a minute, then pour in the salsa from the blender. Add a small amount of water if required.
Cook the chicharrones in the salsa until they have absorbed the salsa and softened. Season and serve.