Grate the rinds of the lemons (yellow part only) and set aside. Squeeze the juice and reserve it. Combine the egg yolks with the reserved rind and sugar. Beat hard until the mixture is light and lemon colored.
Combine the lemon juice and gelatin and let stand for 10 minutes, then heat the mixture over low heat or hot water until the gelatin dissolves. Stir into the yolk mixture.