For the spare ribs:
1) Preheat the oven to 150C/Gas 2.
2) Mix the salt and pepper in a small bowl with the five-spice powder. Rub the mixture all over the ribs and arrange the ribs in a single layer in a roasting pan and slow-roast for 2 hours.
3) In the last 30 minutes of cooking, baste the ribs with the teriyaki glaze. When they are done, the meat will start to pull away from the bone.
4) Just before you're ready to eat, baste the ribs with the teriyaki glaze again and stick them under the grill for 5 to 8 minutes to make the spareribs a nice crusty brown.
5) Separate the ribs with a cleaver or sharp knife, cutting at every second rib so there are 2 bones per piece.
6) Pile them on a platter, and pour on the reserved glaze. Sprinkle with sesame seeds and chopped coriander.
For the teriyaki glaze:
1) In a pot, combine the soy sauce, grapefruit juice, hoisin sauce, ketchup, rice wine vinegar, chilli, garlic, and ginger over medium heat. Bring to a slow simmer and cook, stirring, until thickened, about 20 minutes.
2) Reserve 250ml of teriyaki glaze in a small bowl and set aside