This is a tart lemon curd spiked with limoncello & lightened by whipped cream.
In a med-sized saucepan over med heat, whisk together beaten egg yolks & whole egg, sugar, lemon juice & salt. Switch to a spoon & stir for 10-15 min, or till mixture thickens. You'll know when this happens (it thickens up even more when cooled). Remove pot from heat & stir in butter, afew pats at a time, till it's all used up. Stir in limoncello till incorporated. If you want it perfectly smooth, strain through a fine sieve. Let curd cool & thicken, stirring every so often, then cover & place in the fridge for 1 hr. When curd is cold, whip whipping cream till stiff peaks form. In a lg. bowl, fold whipping cream into the lemon curd, reserving afew dollops of plain whipped cream for garnish. Spoon mousse into lovely dessert glasses, top with a touch of whipped cream & serve with biscotti on the side.