In a large, heavy-bottomed pot, bring all of the marinade ingredients to a boil, then remove from heat and let cool completely. Submerge the chopped raw meat in the marinade and refrigerate, covered, for 48 hours.
Strain the meat and vegetables out of the liquid (retaining the marinade liquid). Separate meat from vegetables and discard vegetables and bay leaf.
In a large, heavy-bottomed saucepan or Dutch oven, heat the garlic in the olive oil just until it turns lightly golden. Add the onion, carrot, and celery and saute until vegetables are softened and onion is transparent, about 6 to 8 minutes. Add the chili pepper flakes and saute for another 30 seconds. Stir in the prosciutto and saute for about 1 minute.
Pat the pieces of meat with a paper towel until dried well, then add to the pot and stir just until browned. Pour in the strained marinade liquid and bring to a simmer, scraping the bottom of the pot with a wooden spoon to loosen any browned bits. Add the bay leaf. prunes and sugar and return to a simmer. Cover and let simmer over low heat until meat is very tender, about 2 hours.
When meat is tender, stir in the orange zest, raisins, pine nuts, and grated chocolate. Stir until chocolate is melted and all ingredients are well combined. Taste and adjust seasoning with salt and pepper, as necessary.
Serve over creamy bowls of polenta, sprinkled with finely chopped fresh parsley.