Place the pork ribs in a heavy lidded casserole dish or a deep pan.
Mix all the sauce ingredients except for the cornflour and spring onions. Whisk until combined and pour over the pork ribs, coating them well.
Cover (use aluminium foil if your dish doesn't have a lid) and roast in the middle of the oven for two hours and a half hours.
After two hours remove the lid from the casserole dish and turn the ribs carefully, basting each one. Return to the oven for 15 minutes and repeat again, turning the ribs so the brown somewhat for the final half hour of cooking.
At the end of the cooking time, carefully drain off the liquid in the casserole dish and place into a small saucepan. Bring to a simmer.
Dissolve the cornflour in a little cold water and add to the simmering sauce mix. Stir well until it thickens, for 2-3 minutes, and then pour over the ribs, coating evenly.
Garnish with chopped sping onion, if desired, and serve immediately.