Soak the gelatine leaves in a bowl of cold water for 2 minutes to soften. Drain the gelatine and gently squeeze out the excess water.
Put the eggs, lemon zest and juice, butter and sugar in a heatproof bowl and mix with a whisk to combine well. Place the bowl over a saucepan of gently simmering water, ensuring the base of the bowl isn’t touching the water. Whis