Lemon Curd Mousse

Directions

1. 1
   In a heavy saucepan whisk together the egg yolks and the sugar, whisk in the lemon juice and the butter, and cook the mixture over moderately low heat, whisking constantly, for 5 to 7 minutes, or until it just reaches the boiling point. (It took me between 10-12 minutes to reach the boiling point. Do not let the mixture boil.)
2. 2
   Strain the curd through a fine sieve set over a bowl, stir in the zest, and let the mixture cool, its surface covered with plastic wrap.
3. 3
   Chill the curd, covered, for at least 4 hours or overnight.
4. 4
   In a bowl with an electric mixer beat the cream until it holds stiff peaks, whisk one fourth of it into the curd to lighten it, and fold in the remaining cream gently but thoroughly.
5. 5
   Transfer the mousse to a serving bowl and chill it, covered, overnight.
6. 6
   **Cook time does not include cooling the curd for 4 hours and the mousse chilling in the refrigerator overnight.