Combine eggs, sugar, passionfruit and lemon juice in a heatproof bowl over a saucepan of gently simmering water. Cook, stirring, for 3 minutes or until sugar has dissolved.

Gradually add the butter, one or two cubes at a time, whisking continuously.

Cook, whisking, for a further 5 minutes or until the mixture has thickened and coats the back of a spoon. Remove from heat. Cover the curd surface with plastic wrap to prevent it from forming a skin. Allow to cool to room temperature, then refrigerate until cold.