Step 1Make small slits evenly over the surface of the pork. Insert a sliver of garlic into each slit. Sprinkle salt and cracked black pepper over the roast and rub in.
Step 2Heat 3 tablespoons oil in a large enameled iron pan. Add the pork and brown well over medium high heat, turning to brown all sides, about 15 minutes total time. Remove the pork from the pan and keep it warm while cooking the vegetables.
Step 3Add another tablespoon oil to the pan and saute the leeks and carrots until tender, 4 to 5 minutes. Pour the hard cider over the vegetables and bring to a boil. Lower the heat to a high simmer and cook until the cider is reduced to 1 cup.
Step 4Return the pork to the pan. Pour the chicken broth over the meat, stir to combine and cook over high heat until the liquid comes to a boil. Turn off the heat; add the bay leaf. Cover the pot and transfer it to a 325-degree oven. Cook until the pork is meltingly tender, about 3 hours.
Step 5While the pork is braising, trim the tops from the fennel bulbs and trim the stem ends. Chop about 2 tablespoons fennel fronds for garnish and set aside. Cut the fennel lengthwise into half-inch slices. Heat the remaining 2 tablespoons oil in a large skillet. Add the fennel slices in batches and brown on both sides. Remove the fennel from the skillet; cover and set aside.
Step 6Add the browned fennel slices to the pork during the last half-hour of cooking.
Step 7Remove the pot from the oven and carefully lift the fennel slices onto a serving platter. Transfer the pork to a cutting board and let it rest while reducing the sauce.
Step 8Skim off any fat from the sauce. Place the pot with the sauce over a burner and bring to a boil. Continue to cook until the sauce is reduced to 1 cup. Strain.
Step 9To serve, slice the meat and arrange it on a platter with the fennel. Spoon sauce over both. Sprinkle with chopped fennel fronds. Combine the toasted fennel seed and fleur de sel and, if desired, sprinkle a pinch over the serving dish. Offer the seed-salt combination to be passed with the braised pork.