1) Preheat griddle or side burner. Heat the oil in a large non-reactive saucepan over medium heat. Add the shallots and garlic and cook until soft. Add the Thai chillis, ginger, curry powder and cinnamon and cook for 2 mins. Add the remaining ingredients and 240ml of water. Cook until the sauce is reduced and thickened about 30 to 40 mins, stirring occasionally. Remove from heat and let cool slightly.
2) Place plum mixture, in 2 to 3 batches, in a food processor and process until smooth, strain into a bowl and let cool to room temperature.
3) Bring water, soy, ginger, peppercorns, coriander, mustard seeds and salt and pepper, to taste, in a large saucepan and bring to a simmer.
For the ribs:
1) Preheat griddle to medium-high heat and preheat oven to 210C/Gas 7.
2) Rub oil on both sides of the ribs. Then rub each rack with the Asian rub. Place racks onto preheated griddle and allow to cook only until griddle marks have been made.
3) Divide the water and soy sauce mixture between 2 roasting pans, place the ribs on a baking rack and set over the liquid in the pan. Roast the ribs in the preheated oven until about 3/4 of the way cooked, about 45 mins, basting every 15 mins.
4) Heat the griddle to high. Transfer the ribs to the griddle and griddle until the ribs are tender, about 45 mins longer, brushing with the glaze during the last 10 mins of cooking. Remove from the griddle and brush with more of the glaze. Slice into ribs and garnish with spring onions.
For the Asian rub:
1) Whisk all ingredients together.
* Chef's Note: If you cannot find ripe plums you can always use canned plums. If you cannot find plum juice you can always use cranberry juice.