Preheat oven to 240°C. Put pork in a large roasting dish on a wire rack. Rub oil over rind. Sprinkle with fennel seeds and salt and rub over evenly. Roast for 20 minutes or until rind bubbles and crackles. Reduce heat to 180°C. Continue to cook for 4 hours or until juices run clear when pierced through to the bone with a metal skewer.
To make stuffing; heat oil in a large non-stick frying pan over a medium heat. Add onion, fennel seeds, garlic and bacon, and cook, stirring occasionally, for 8-10 minutes or until soft. Transfer to a bowl.
Add apple, breadcrumbs, walnuts and sage and stir until combined. Add butter and egg and mix with your hands until mixture becomes sticky when squeezed into pieces. Roll heaped tablespoons into balls and place on an oven tray lined with baking paper.
Spray stuffing balls with oil and bake with pork in the last 35 minutes of roasting, turning twice, or until evenly golden. Transfer pork to a serving platter and allow to stand for 15 minutes. Pour pan juices into a bowl and allow to settle. Skim visible fat layer off the top and discard. Reserve juices for gravy.
Put roasting dish over a medium high heat and add cider. Bring to a simmer for 5 minutes. Combine flour and ¼ cup of stock in a large jug with a fork until smooth. Add another 1¼ cups of stock and stir until combined.
Gradually pour stock onto simmering cider, whisking constantly until combined. Whisk in reserved pan juices and cook until thickened and smooth. Add more stock if gravy is too thick. Strain gravy through a sieve into a clean bowl. Pour into a jug for serving. Serve pork with crunchy stuffing and apple gravy.