Prepare the meat. Notice the fat—don’t trim it off! Combine pork, liver, vegetables, and seasonings. Marinate overnight.In a large pot, cover mixture with water and bring to a boil. Reduce heat and simmer until meat is tender, 1½ to 2 hours. Remove pot from heat and strain, reserving liquid. Allow mixture to cool slightly, then put all through a meat grinder with a course die.Place the ground meat in a bowl and mix in the cooked rice, parsley, scallions, and salt and pepper to taste. Add the reserved cooking liquid, 1 cup at a time, until mixture is moist but not juicy.Stuff the boudin into the casings and link off to approximately 6-inch links. Allow boudin to dry in the refrigerator, uncovered, overnight. This will allow the casing to firm up and better maintain their shape when poached.Separate the links and place the boudin into heatproof plastic bags. Drop into a crock pot filled with hot water on high for 20 minutes. Turn crockpot to low and cook for up to 1 hour. You can also poach in just simmering water for the same amount of time then serve immediately.To eat, pinch one end of the casing between your fingers and bite the boudin from the other end. Using your teeth squeeze the meat out of the casing and into your mouth. Twist the pinched end to force the meat up toward the open end and bite it again.