Put the salt, paprika, all purpose spice, oil and black pepper in a cup. Stir well.
Cut the onion heads into slices.
Cut the pork into steaks about 1 1/4″ (3 cm) thick. Then tenderize them on both sides with a meat mallet. If you don't have one, use the bottom of a beer bottle and a wooden board.
Put them in the preferred container - a tray or pot, and pour on the marinade. Add enough milk to cover the steaks.
Stir everything very well with your hands for the spices to soak into the meat well. If using a tray, cover it with foil; if using a pot, put the lid on. Leave them to sit for 24 hours.
After the time has elapsed, prepare them for baking as follows. Arrange just the steaks and marinade, without the onions, in an oven dish. Don't throw out the onions though. Sprinkle each steak with soy sauce on both sides. Then, wrap them in aluminum foil.
Put them to bake in a preheated 392°F (200 °C) oven. Bake for 1 hour, then remove the foil and add the onions. Return to the oven to finish baking - until you feel they're ready.