Mix salt, lemongrass, spices, garlic, ginger, and chillies, then rub into the pork flesh.
Cover and marinate in the fridge for 2 to 12 hours.
Vacuum-pack the pork and cook in an 85°C water bath for 5 hours.
Strain and save the cooking liquor, then let the pork cool.
Flatten the pork between trays with weights and chill for 1 to 2 hours.
Preheat the oven to 180°C.
Fry the pork skin-side down in rapeseed oil for 15 minutes, then roast for 10 minutes.
Boil the strained liquor with 200ml of water and season with soy and sesame oil.
Cook cabbage with butter and 3 tablespoons of water in a lidded pan for 7 minutes.
Serve the pork on the cabbage and pour the hot juices over.