Barbecue prawns

Name: Barbecue prawns
Prep time: 10 min
Cook time: 20 min
Total time: 30 min
Cuisine: Australian
Ingredients: 400 gm canned peeled tomatoes; 75 gm brown sugar (1/3 cup); 60 ml cider vinegar (¼ cup); 2 tbsp Worcestershire sauce; 1 tbsp Dijon mustard; 3 garlic cloves, finely chopped; 2 tsp each ground coriander and ground cumin; ½ tsp each ground cinnamon, ground fennel and sweet paprika; ¼ tsp ground cloves and ground chilli; 80 gm butter, coarsely chopped; 2 kg uncooked large prawns (about 20), split lengthways, tails intact, deveined, heads discarded; 2 tbsp finely chopped chives