Cook the Aromatics: Heat the butter in a large pan over medium heat. Add the chopped onion and sauté until softened and translucent, about 4-5 minutes.
Add Garlic and Ginger: Stir in the minced garlic and ginger, cooking for another 1-2 minutes until fragrant.
Add Spices: Add the garam masala, ground cumin, and curry powder. Cook for 1-2 minutes, stirring frequently to toast the spices and release their aromas.
Tomatoes and Simmer: Add the crushed tomatoes and red chilli powder. Stir to combine, then bring the mixture to a simmer. Cook for about 10 minutes, allowing the sauce to thicken slightly.
Season and Add Coconut Milk: Stir in the brown sugar, salt to taste, and coconut milk. Mix well and let the sauce simmer for another 5 minutes.
Cook the Prawns: In a separate pan, heat the vegetable oil over medium heat. Add the King prawns and cook for 3-4 minutes until they turn pink and are cooked through. Then, add the prawns to the curry sauce and stir to coat them evenly.
Final Simmer: Let the curry simmer for an additional 2-3 minutes to allow the flavours to meld together.
Serve: Garnish with fresh coriander leaves and serve the curry hot over cooked jasmine rice.