50g/2oz/4 tbsp golden caster (superfine) sugar
3 medium egg yolks
125ml/4fl oz/½ cup double (heavy) cream
grated zest and juice of 1 lemon
1 Stir the sugar and 125ml/4fl oz/½ cup water in a pan over a low heat until dissolved. Increase the heat and boil for 7–8 minutes until the syrup reaches 105°C/221°F on a sugar thermometer.
2 Whisk the egg yolks in a bowl and gradually whisk in the hot syrup in a thin stream. Beat until thick, mousse-like and cool.
3 Whisk the cream until it forms stiff peaks, then add the lemon zest and juice and whip again to form soft peaks. Fold into the mousse mixture. Cover and chill in the refrigerator. Whisk well before serving.