Using a 6cm (2½in) pastry cutter, cut out 12 x 6cm (2½in) rounds of bread. Lightly butter the rounds and top with a lettuce leaf.
Make a dressing for the prawns by combining the mayonnaise, ketchup, lemon juice, Tabasco and freshly ground black pepper in a bowl.
Put 1 teaspoon of the mayonnaise mixture on each round of bread and top with some prawns. Serve dusted with a little cayenne pepper and a slice of lemon.
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