Marinate pork with 1/2 cup of fish sauce. I used Rufina patis.
In a large size cooking pot, heat oil and then sautee' garlic until light brown.
Add in onion and sautee' until transparent.
Add the marinated pork shoulder and cook in low heat. cover and cook until all of the liquid has evaporated. About thirty minutes.
Add the Anaheim pepper, large intestine and pork blood and whisk right away to prevent coagulation. Cover and let it simmer in medium heat. Add the vinegar and bay leaves if using. After adding the vinegar, don't mix the ingredients. Just cut through the ingredients to incorporate the liquid.
Cook in low heat for additional 45 minutes or until the color changes to brown.
Adjust taste by adding fish sauce and vinegar. Season according to your taste.