To make the marinade: In a small bowl combine all marinade ingredients. Place prawns in a resealable plastic bag in a shallow baking dish. Pour marinade over prawns; close bag. Marinate in refrigerator for 30 minutes, turning occasionally to distribute marinade.
Meanwhile, make sauce in last 10 minutes of marinating time: In a saucepan melt 1 tablespoon of the butter. Add wine and shallots; cook rapidly over high heat until liquid has almost evaporated. Add cream, tomato, and paprika; cook over medium heat until mixture is reduced and slightly thickened. Add remaining butter; stir until melted. Remove from heat and cover to keep warm.
Remove prawns from marinade; discard marinade.
Place prawns on cooking grate. Grill 6 to 8 minutes or until prawns turn pink and are opaque in thickest part (cut to test), turning once halfway through grilling time. Serve with warm sauce.