For the syrup:

Mix water and sugar in a small sauce pan. Bring to a boil. Turn off the heat and add the limoncello. Place in refrigerator to cool (it can be made several days in advance).

For the cream

Place lemon juice, lemon zest and sugar in a sauce pan over medium heat.

Bring it to a boil and let it cool slightly. In a clean bowl beat the yolks to combine.

Dribble a small amount of hot lemon mixture in a steady stream into the yolks while quickly whisking the two together.

Continue to dribble in the lemon mixture and whisk until you feel, with your hand, that the bowl's side or bottom has become warm or as close as possible to the liquid's temperature. Continue to add the rest of the hot liquids in a steady stream to the yolks while whisking (this process is called tempering and it is done to avoid cooking the yolks).

Cook the mixture over moderately low heat, whisking frequently, until cream is thick enough to hold marks of whisk and first bubble appears on surface, about 6 minutes.

Stir in butter and limoncello. Transfer lemon cream to a bowl and let it cool to room temperature or below. Cover it with plastic wrap. At this point you can refrigerate the mixture for 2 or 3 days until you are ready to assemble the tiramisu.

Assembling the ingredients

Mix mascarpone cheese and powdered sugar in a clean bowl until soft.

Add to the Lemon Cream (at room temperature). Mix until smooth. Do not over whip when using mascarpone cheese or it will separate.

Fold whipped cream (soft peaks) into above yolk/mascarpone cheese mixture.

Dip ladyfingers in the limoncello Syrup for ½ minute on each side and then alternate layers of lady fingers soaked with simple syrup and cream in a 8 x 12 pan.

Begin with cookies and finish with cream.

It is best to assemble several hours before cutting.

Store in refrigerator until ready to serve.