Freeze the beef heart (or thaw, if it's already frozen) to about 32°F, but to no cooler than that. Note: If adding the optional beef kidney or ground beef, freeze them them the same way.
Refrigerate the onion.
Trim the harder fat from the frozen beef heart.
Cut the frozen heart into 1” slices.
Grind the beef heart it before it thaws too much. Note: If adding the optional beef kidney or ground beef, grind them in with the beef heart.
Put the ground beef heart into a freezer bag and distribute in the bag to an even thickness.
Refreeze the ground beef heart.
Follow the directions on the package for the textured vegetable protein to reconstitute enough to measure out one cup. Set the measured cup aside, and refrigerate any that’s left for later use.
After making sure the heart is down to about 32°F again, remove the frozen ground beef heart from the freezer.
Grind the refrozen heart a second time.
Add one cup of the prepared textured vegetable protein to the meat and mix well.
Remove the onion from the fridge, mince it fine, and set it aside.
In a sauce pan, melt the cup of shortening over medium-high heat.
Sauté the minced onion in the melted shortening for about one minute, until the onion is translucent.
Reduce the heat to low, add the meat mixture to the sauce pan and blend well.
Simmer the sauce over low heat for 30 – 45 minutes, until the meat is tender but is also still slightly juicy.
Add the paprika, chili powder, and ground cumin into the meat mixture and stir well for even distribution.
Adjust the spices for personal taste as desired and simmer a bit longer before serving.