2) In the meantime, place the salt, sugar, water and chilli flakes into a pan and heat just until the salt and sugar have dissolved. Turn the pan off and add the ice. Stir until the brine has cooled.
3) Place the prawns into a 4.5L sealable bag and pour over the brine. Place in a container and set in the refrigerator until the wood chips are done soaking, approximately 45 more minutes.
4) While the prawns are brining, heat 2kg of charcoal in a chimney starter until the coals are covered with a white ash.
5) After the chips are done soaking, drain them and set aside. Drain the prawns in a colander and thread on 4 to 6 rounded skewers.
6) Carefully transfer the charcoal to a large, 46cm round, stainless steel bowl. Cover the charcoal with the wood chips. Lay the skewered prawns directly atop the chips making sure that the prawns do not come in direct contact with the charcoal and that the prawns are in 1 layer. Turn another, smaller (33 to 36cm) metal bowl upside down on top of the prawns. Cook for 15 to 20 minutes or until cooked through. Serve warm or chilled.
For the dipping sauce:
1) In a small bowl whisk together the mustard seed, dry mustard and water.
2) Place the mustard and water mixture into a small saucepan and add the remaining ingredients. Bring to a simmer over high heat. Do not allow to boil. Remove from the heat and puree with a handheld blender for 5 to 10 seconds while drizzling with oil, leaving some of the seeds intact if desired.
3) Pour into a glass jar or container, allow to cool, cover and allow to sit in refrigerator overnight before using. Store in the refrigerator for up to 1 month.
Yield: approximately 250ml.