Add the mascarpone, powdered sugar, and lemon zest to a large bowl and beat with an electric mixer on medium-high for 4 minutes, or until fluffy.

Reduce your mixer speed to low and gradually add in the chilled heavy cream.

As the mixture thickens, increase the speed to medium and beat until medium peaks form (you want the peak to hold its shape, but that the tip still curls a bit when you lift up the beater).

Transfer about two-thirds of the mixture to another large bowl. Fold in 1/2 cup of the lemon curd.

Cover the original bowl containing the remaining mascarpone mixture with plastic wrap and chill until you're ready to unmold and frost the cake.

Now you're ready to layer the cake. Line your 9x5" loaf pan with plastic wrap, leaving overhang on all sides.

Add a single layer of graham crackers to the bottom of the prepared loaf pan, breaking as needed to fill the bottom.

Spread about a quarter of the lemon cream mixture over the graham crackers.

Dollop about 1/2 cup of the jam over the lemon cream layer and gently spread over the lemon cream.

Dot 1/4 cup of the lemon curd over the jam.

Add another layer of lemon cream mixture over the curd.

Top with another layer of graham crackers.

Repeat this process -- a layer of lemon cream, 1/2 cup jam, remaining lemon curd.

Finish off with the remaining lemon cream over the curd, then top with another layer of graham crackers.

Cover with plastic wrap and add to your freezer for at least 6 hours. Cover and chill the remaining jam until ready to serve the cake.

After 6 hours, uncover the cake and invert the pan on to the platter. (I found it helpful to first run a knife around the edges of the pan, in between the pan and the plastic wrap.) Using the plastic overhang to help you, unmold the cake and peel off the plastic wrap.

Frost the cake with the reserved mascarpone mixture.

Freeze for at least 15 minutes. Just before serving, mix blueberries into the reserved jam and spoon over cake. This cake can be made 2 days ahead, and kept in the freezer. Slice into 8 pieces to serve.