For the Boudin:
Braise the pork shoulder with the onions, garlic, celery, hot peppers, salt, pepper, and cayenne. Once the pork is tender, separate the meat and vegetables from the cooking liquid and reserve the liquid.
Push the meat and vegetables through a coarse die in a meat grinder; place into a mixing bowl, and combine with the rice. Adjust the consistency with the reserved cooking liquid and season with fresh parsley and chopped scallions. Pipe the boudin into rinsed natural casings and twist off into links. The links can be poached, grilled, pan fried, or eaten cold. They can also be uncased, rolled into balls, breaded, and deep fried.
To Assemble and Serve:
Serve the Boudin with Abita mustard and bread-and-butter pickles.