Heat oven to 180C/160C fan/gas 4. Lay the pork, skin-side up, on a shallow baking tray and sprinkle liberally with flaky sea salt. Cover with baking parchment and lay a second baking tray on top. Put a weight on top of the tray (such as a casserole dish), then put in the oven. Bake for 40 mins, then turn the oven up to 200C/180C/gas 6 and cook for another 20 mins or until the skin is deep golden and crisp. If it’s not quite ready, return to the oven and check every 10 mins.
Remove the crackling from the parchment and leave it to rest on a cooling rack. Spoon 2 tsp of the leftover pork fat into a large mixing bowl with the white pepper, sesame oil and oyster sauce to make a dressing. Bring a large pan of water to the boil, then add the beansprouts and cook for 3 mins until just hot through. Drain, then put the sprouts into the bowl with the dressing and mix well. To serve, break up the pork crackling and sprinkle liberally on top.