8 ounces mascarpone or plain whole-milk Greek yogurt, room temperature
3/4 cup powdered sugar
2 tablespoons finely grated lemon zest
2 1/2 cups chilled heavy cream
1 cup homemade or store-bought lemon curd, divided
16 graham crackers, divided
1 1/2 cups Blueberry Jam, divided
1/3 cup fresh blueberries
Line a 9×5″ loaf pan with plastic wrap, leaving overhang on all sides. Using an electric mixer on medium-high speed, beat mascarpone, powdered sugar, and lemon zest in a large bowl until fluffy, about 4 minutes. Reduce speed to low; gradually add cream. Increase speed to medium as mixture thickens; beat until medium peaks form. Transfer two-thirds of mascarpone mixture to another large bowl and fold in ½ cup lemon curd. Cover remaining mascarpone mixture; chill until ready to unmold and cover cake.
Place a single layer of graham crackers over bottom of prepared pan, breaking as needed to fit. Using a small offset spatula, evenly spread a quarter of lemon cream over graham crackers. Dollop 1/2 cup jam over top, then gently spread evenly over lemon cream. Drizzle 1/2 cup lemon curd over. Spoon a third of remaining lemon cream over curd and top with another layer of graham crackers. Repeat layering process with half of remaining lemon cream, 1/2 cup jam, and remaining lemon curd. Finish with a final layer of lemon cream, then graham crackers. Cover with plastic wrap; freeze at least 6 hours. Cover and chill remaining jam until ready to serve cake.
Uncover cake and invert pan onto a platter. Using the plastic overhang to help you, unmold cake; peel off plastic. Spread top and sides of cake with reserved mascarpone mixture (if mixture looks a little loose, whisk until soft peaks form before using). Chill in freezer at least 15 minutes.
Just before serving, mix blueberries into reserved jam and spoon over cake.
Do Ahead: Cake can be made 2 days ahead. Cover and keep frozen.
Recipe by Nicole Rucker