Preheat oven to 300°F (150°C).
On a large plate, pat brisket with paper towels until dry. Season liberally with kosher salt and black pepper.
Heat a large Dutch oven to medium-high. Add a good drizzle of extra virgin olive oil, then, sear the brisket until it’s golden brown on all sides. Set brisket aside.
In the same pot, cook sweet onion, celery and carrot in the residual oil for 2-3 minutes, until partially cooked.
Add ground fennel and black pepper, and bloom on low heat for 30 seconds, stirring constantly. De-glaze with red wine. Cook the wine on low heat until it’s almost completely reduced and cooked off, stirring occasionally.
Add beef stock and prunes and bring the stock to a simmer. Return the brisket to the pot, spoon the sauce + prunes over the top of it.
Add rosemary and cover with two layers of foil and seal the sides neatly so the heat doesn’t escape.
Cook the beef for 3-4 hours until tender. (You should be able to tear apart with two forks or insert a cake tester without much resistance).
Rest the brisket in the hot prune sauce for 15 minutes, then remove the brisket and reserve on a large plate, covered with foil.
Reduce the prune sauce until it has thickened and coats the back of a spoon. Add the red wine vinegar, and season to taste.
To serve, plate parmesan polenta, add sliced brisket, and top with the prune sauce draped on top. Garnish with chopped parsley. Bon appetit!