Mix the ingredients for the first marinade in a large bowl, toss in the prawns and coat them well with the marinade. Allow them to rest for 15 minutes.
Mix together the ingredients for the second marinade in a separate bowl. After 15 minutes remove the prawns from the first bowl, gently lift them to make sure any excess moisture has dripped off and then put them into the second marinate. Ensure that the prawns are well coated with the marinade, cover the bowl and rest in the fridge for 1 hour.
Preheat the oven to 200°C and place your oven rack on the topmost rung of the oven with a tray underneath to catch any drips.
Gently thread about 5-6 prawns on each skewer(depending on the length of the skewers), and place them side by side on the rack making sure that they don't overlap. Grill the prawns for 3 minutes on each side. Once they're cooked, baste them with melted butter and grill for another minute before serving.