Add the oil to a large skillet over medium-high heat. When hot, add the prawns, sprinkle with salt and pepper and saute until the prawns turn bright red and the edges are golden, 3 to 5 minutes. Remove and keep warm.
Add the butter to the prawn pan and when it begins to foam, add the ginger, apple slices and onions. Cook until the apples are caramelized, about 10 minutes, stirring to break up the apple chunks. Add the garam masala, coriander seeds, paprika, turmeric, chili flakes and a pinch of salt and cook for 1 minute. Pour in the apple cider and chicken stock and reduce by one-third, about 10 minutes. Pour in the coconut milk, stir well and continue to reduce until it thickens and coats the back of a spoon; this should take 3 to 5 minutes. Add the prawns and stir to heat through. At the last minute, stir through the basil leaves until they are just wilted. Serve the curry with rice and garnish with fresh basil sprigs.