To make the macadamia salt and pepper dust, dry roast combined sea salt and peppers in a heavy-based pan over medium heat. Stir until aromatic and lightly toasted, remove from the heat and cool. Use a mortar and pestle or spice grinder to crush to a coarse powder. Pour into a bowl and stir through the macadamias. Set aside.
Sift the flour, baking powder and salt into a large bowl and mix well. Make a well in the centre and gradually whisk in the beer until the batter reaches the consistency of thickened cream (you may not need all of the beer).
Heat the macadamia oil in a wok or deep fryer to 190°C or until a cube of bread turns brown in 15 seconds when added to the oil.
Pat the fish fillets dry with a paper towel, dust lightly with the extra flour and dip 2 pieces of fish, 1 at a time, into the batter to coat.
Drain off any excess and deep-fry the fish for 3 to 5 minutes, depending on the size and thickness of the fillets, until golden brown and cooked. Drain on absorbent paper and immediately sprinkle each cooked fillet with a teaspoon of macadamia dust.
Repeat until all the fish is cooked, reheating oil between batches and keeping the cooked fillets warm.