Put the beef in a large covered stainless-steel pot or stainless pressure-cooker insert. Add filtered water to cover the meat by about 2 inches, then add the tenderizing salt.
Choose one tenderizing route. Stovetop: cover and maintain a gentle simmer for 2 to 3 hours, adding water if needed, until the beef yields to a fork. Pressure cooker: seal according to the appliance instructions, cook on high pressure for 35 minutes, and use either the natural- or quick-release branch from the source.
Lift the beef from the liquid with a stainless-steel handled strainer or slotted spoon. Drain until cooking broth is no longer pooling around the pieces. Keep the liquid labeled as cooking broth, not GAPS meat stock.
Optional fat recovery: rest the cooking broth for about 10 minutes. Ladle it through a fine stainless-steel strainer into a clean glass container without pressing solids or adding cloudy bottom sediment.
Set the glass container in an ice bath and stir until the broth no longer steams. Refrigerate overnight, then lift off the firm fat layer for frying. Keep the remaining liquid labeled as cooking broth.
Heat a dry stainless-steel or well-seasoned cast-iron frying pan over medium heat until hot but not smoking. Add enough tallow or duck fat to coat the pan when melted.
Spread the drained beef in one uncrowded layer, using two pans or batches if needed. Press tall pieces slightly flatter and season with half of the frying salt.
Let surface moisture evaporate, lower the heat, and fry the first side for 25 to 30 minutes. It is ready to turn when the underside is deeply brown and crisp and releases with a firm scoop instead of tearing.
Turn every piece. Add the remaining frying salt and optional pepper or dried ginger. For the Mexican-style branch, add the cumin, oregano and optional chili powder, distributing the spices evenly.
Fry the second side over low heat for 20 to 25 minutes, until crisp and brown outside with moist tender centers. Serve promptly or hold warm.