How to Make It
In a medium heatproof bowl, whisk the eggs with the sugar, lemon zest and lemon juice. Set the bowl over a saucepan of simmering water and whisk over moderate heat until thickened, about 6 minutes. Whisk in the gelatin until melted. Remove from the heat and whisk in the butter. Strain the lemon curd through a fine sieve and refrigerate until chilled and set, about 1 hour.