Preheat the oven to 300. If using fat caps, or a very fatty cut, freeze the meat for 30 minutes to firm up. Dice the meat with a heavy knife into ½ inch cubes.

Put the meat into a braising pan, like a dutch oven, and bake for 2.5-3 hours, or until the fat is nearly completely rendered, mashing the meat around carefully with the back of a wooden spoon or potato masher here to speed the process and make a mash of cracklings.

Resist the urge to put the pan on the heat to render the fat quicker if you want to reserve the leftover fat for cooking (there could be 2-4 cups depending on the cuts you use). When the fat is rendered, carefully strain the meat and return to the pan, and continue to crisp on low heat while you toast the ingredients for the guajillo sauce.

For the guajillo sauce, in a cast iron skillet or on a grill, toast the dried chilis on each side until lightly colored. Remove the chilis, crack them open, discard the seeds from the chilis, and combine with the lamb stock and rehydrate.

Remove the chilis, then add the onion, cut side down, along with the unpeeled garlic cloves and tomatillos.

Lightly char the onion, tomatillo and garlic cloves over medium heat, then remove the peel from the onion and garlic cloves and put in a blender with the tomatillo, salt, chilis and their liquid. Puree the mixture until very smooth, then pour into the pan with the cracklings, simmer for 10 minutes.

Double check the seasoning, chill completely and reserve until needed. The braised cracklings will keep for 5 days. Serve on masa cakes, or as a taco or tomale filling.