Put the lemon juice, 1 cup of the limoncello, ½ cup sugar and the water in a small saucepan and bring to a boil.  Let it boil for about 4 - 5 minutes, stirring constantly to dissolve the sugar, then set aside and allow to cool completely.

Put a medium/large pot of water to boil, then in a heat safe bowl that is large enough to fit on top of the pot, beat together the egg yolks, ¼ cup of lemon curd, the lemon zest, th¼ cup of sugar and ½ cup of the limoncello.

Put this bowl over the boiling water, and whisk constantly, scraping down the sides for about 5 minutes, or until the mixture thickens and makes ribbons when dropped on the surface.  Remove from heat and allow to cool.

Put the egg whites and remaining ¼ cup of sugar in a bowl, and use an electric mixer to beat until firm peaks form and set aside.

Put the mascarpone in a large bowl, and stir with a wooden spoon until broken up and soft.  Add the cooled egg yolk/lemon mixture and gently fold together with a spatula.  Begin to fold in the egg whites a little at a time, until the mixture is light and completely blended.

Pour some of the cooled syrup into a small dish - no deeper than ¼".  Begin to gently soak the lady fingers - one at a time - by rolling them gently in the syrup.  Don't leave them in the syrup long as they will fall apart.

Line the bottom of a 9x13" casserole dish with an even layer of lady fingers, then spread ½ of the mascarpone mixture evenly over the top.  Repeat with another layer of lady fingers and custard, then cover and refrigerate overnight or for at least 4 hours.

Before serving, sprinkle blueberries over the top.  Whisk together about ¼ cup more of lemon curd with some limoncello until runny, then drizzle this over the top of the blueberries