For sauce, stir ginger into creme fraiche or sour cream; thin with milk to consistency of syrup, set aside. Preheat a baking tray and your serving plates in a 160F oven.
For chili oil sauce, heat 2 tablespoons vegetable oil in skillet over medium heat. Saute chili flakes and garlic just until fragrant, add wine and ginger. Raise heat to high; reduce mixture to about 3 tablespoons. Meanwhile, stir together soy sauce, vinegar and arrowroot to form a slurry. Add slurry to reduced wine mixture; bring to a boil to thicken sauce slightly. Sprinkle sugar over sauce, adjust to taste. Remove from heat. Cover, keep warm.
Pat prawns dry with paper towel. Heat one tablespoon chili oil in saute pan over high heat. Saute prawns in hot oil just until opaque. Transfer to warmed tray in 160F oven. Add remaining tablespoon chili oil to skillet. Cook pineapple until slightly browned. On preheated plates, arrange prawns on pineapple, drizzled with chili oil and ginger creme fraiche. Garnish with spring onion.
Serves 4 as a main dish.