The recipe says that the sugar syrup must reach 120C, but I have no sugar thermometer. Can it be done without a thermometer?
Dissolve the sugar in a medium saucepan with 120ml boiling water. When clear, bring to the boil and place a sugar thermometer in the pan.
Meanwhile, whisk the yolks with an electric mixer until creamy. When the sugar syrup reaches 120C, remove from the heat at once. Keep the mixer beaters running, drizzle the syrup onto the yolks and beat, on full speed, for 3-5 mins until you have a firm yellow foam. Remove and cool, whisking occasionally. Divide into 3 portions.