This tripe soup is usually sold on weekends in small mom-and-pop kitchens called "Fondas", or in restaurants that specialize in Typical Mexican antojitos. The tripe soup is called different names depending on the region. It is known as "pancita", Mondongo, or Menudo.”
Simmer the cow feet and marrow bones in a large pot with 6 quarts of water, 4 garlic cloves and an onion for about 15 minutes at medium heat without covering. During this time, skim off the foam that forms.
Add the tripe and oregano and cook for about 2 – 2 ½ hours approximately until tripe is tender but firm (make sure you do not overcook). For the INSTANT POT, cook for 30 minutes. For a Pressure cooker 45 minutes. You could also use a slow cooker and set it in low for 6 hrs.
Remove the cow feet and marrow bones from the pot. Skim the fat that forms on top of the broth. Once the Cow foot cools a little, remove the bones and chop the meaty parts of to be returned to the pot.
While the meat is cooking, prepare the guajillo sauce. Toast the Guajillo peppers in a griddle over medium heat. Press them down with a spatula slightly toasting them without burning them.
Place the roasted peppers in a bowl and cover with water. Let them soak for about 25 minutes until soft. After that, drain the peppers and place them in your blender with 3 garlic cloves, ½ cup of the broth, and cumin if using. Blend until very smooth. Strain the sauce using a sieve and pour into the pot. Simmer the broth for another 30 minutes, partially covered. Taste to season with more salt if needed.
Serve the soup in large bowls and place the garnishes in a dish in order for everyone to add to their liking. Do not forget warm corn tortillas to soak in the broth.