Add wine, red onion, garlic, rosemary, thyme, bay leaves, crushed fennel seeds, and red pepper flakes to a large glass or other non-reactive bowl and stir to combine.
Add pork chunks to bowl and turn until each piece is covered. Cover and place bowl in the refrigerator for at least 8 hours. Turn pork occasionally while marinating to evenly distribute flavors.
To prepare, remove bowl from refrigerator and remove pork pieces from marinade. Pat dry with paper towels and set aside.
Separate the marinade liquid from the solids and reserve both, discarding the woody herb stems and bay leaves. Set aside.
Heat the olive oil in a large heavy-duty skillet or Dutch oven over medium-high heat. Add the marinated pork and sear until evenly browned on all sides, approximately 8-10 minutes. Season with salt and black pepper, to taste.
Add the solids from the marinade and cook until onions are soft and translucent, approximately 10-12 minutes, stirring frequently.
Add liquid from marinade to skillet and scrape up the brown bits from the bottom of the pan. Continue cooking until liquid is reduced to approximately one third of its original volume.
Add tomatoes and 1 cup chicken broth and stir to combine. Cover and reduce heat to medium-low and cook for 2 to 2½ hours, stirring every half hour or so. Add more chicken broth, if needed, while cooking.
When pork can be pulled apart easily with a fork, remove from heat and let rest in warm juices for 10-15 minutes. Serve immediately over a bed of creamy polenta and garnish with chopped fresh parsley, if desired.