Step 1 Process flour, egg, coconut milk and 2 tablespoons fish sauce in a food processor with 1 teaspoon salt until very smooth. (It should be the consistency of thickened cream - if too thick, add 1-2 tablespoons cold water.) Place in a bowl. Set aside while you make the salad. Step 2 Place sugar, lime juice, lime leaves, chilli and remaining 3 tablespoons fish sauce in a bowl. Stir to dissolve sugar. Toss dressing with tomato, onion, mango and cucumber. Step 3 Half fill a saucepan or deep-fryer with oil and heat to 180°C (test with a cube of bread — it will turn golden in 30 seconds when ready). Place extra flour in a bowl and season. Dip the fish in the flour, shaking off excess, then in the batter. Fry, in batches, for 2-3 minutes until golden, turning with tongs if necessary. Drain on paper towel. Serve with salad and lemon.