Whipped cream and fresh mint leaves, for garnish
Combine eggs and sugar in a large mixing bowl and beat with the electric mixer until thick and lemon colored, 5 to 8 minutes.
Beat in the melted butter by pouring in gradually in a thin stream and mix in the lemon and lime juices.
Pour into top of a double boiler and cook, whisking constantly for about 15 minutes or until mixture is hot and thickens.
Transfer to a bowl and chill, covered, for 1 hour. Stir a couple of times.
Beat the cream until soft peaks form. Fold into the chill mixture along with the zests.
Spoon into stemmed glassed and top with rosettes of whipped cream, a thin slice of lemon and a sprig of mint.