For anchovy coulis, heat olive oil in a saucepan over low heat. Add onion and garlic and stir occasionally until soft and caramelised (10-15 minutes). Add anchovies and cook until dissolved (3-5 minutes), then deglaze pan with vinegar and wine until reduced (1-2 minutes), then add fish stock and cook until reduced by half (2-3 minutes). Cool to room temperature. Blend in a blender until smooth. Stir through mayonnaise and season to taste. Makes about 300ml.
Place prawns cut-side up on a tray. Lay an anchovy half on each halved prawn, press down firmly and set aside.
Combine oil, garlic, rind, juice and paprika in a bowl. Season to taste, brush over prawn flesh, cover and refrigerate until required.
For sherry and truffle dressing, warm port, sherry vinegar and sugar in a small saucepan over medium heat until sugar dissolves (1-2 minutes). Cool, add remaining ingredients, season to taste and set aside. Makes 165ml.
Heat a char-grill pan or non-stick frying pan with a little olive oil over high heat. Cook prawns cut-side down for 2 minutes, then turn and cook for another 30 seconds. Remove and arrange on a serving platter.