In a bowl, whisk the whole eggs and egg yolks together and set aside.
In a heavy bottomed sauce pan combine the sugar, lemon zest, juice and egg mixture together and whisk on a medium low heat until mixture thickens and can coat the back of a spoon. About 15-20 minutes.
Stir in butter and then remove from heat when it's melted.
Pour the lemon curd through a fine mesh strainer into another bowl straining out any lumps. Press plastic wrap directly into the lemon curd and cool to room temperature before using.
To make the filling:
Scoop out 1/4 cup of the cooled Lemon Curd and set aside.
In a large mixing bowl combine the remaining cooled lemon curd with the softened mascarpone cheese. Mix with an electric mixer on medium-high speed until smooth. Set aside.
Using clean beaters in a separate bowl combine the heavy cream and confectioners sugar and beat until stiff peaks form.
Fold half of the whipped cream into the mascarpone/lemon curd mixture until well combined. Set aside.
To make the soak:
In a shallow dish with high sides combine the Limoncello and water.
Dip each lady finger cookie into the Limoncello mixture and lay them into a 9x13 pan (I used a glass Pyrex) break the cookies to fit them in if necessary. I did two rows of 7 cookies vertically and two rows of 2 cookies horizontally, but just make sure the cookies fit nicely together.
Spoon 1/2 of the lemon filling over the first layer of cookies. Add another layer of cookies and spread the remaining lemon filling over them. Add a third layer of cookies and top with the remaining whipped cream.
Using the remaining 1/4 cup of lemon curd, spoon it over the top of the whipped cream and use the back of a small spoon to make swirly designs. Decorate with fresh lemon slices.