Toss the prawns in a bowl with the vegetable oil and a little seasoning, and heat a large frying pan until hot. Tip in the prawns and cook for 2-3 minutes or until charred at the edges.
Turn the heat down to medium and add the butter. Once foaming, add the garlic and ginger, and cook for 2 minutes, then add the spices and cook for a minute, while stirring. Simmer for several minutes until the prawns are cooked through, then add the lime juice and fish sauce to taste. Tip into a serving bowl and stir through the coriander. Serve with a baguette to mop up the buttery juices, if you like.