In a medium pot over medium-high heat, cook blueberries, water, cornstarch, and 1/4 c. confectioners’ sugar, mashing down on blueberries, until bubbling and thickened and berries are mostly broken down, 6 to 8 minutes. Remove from heat and stir in lemon juice. Let cool.

Meanwhile, in a large bowl, using a handheld mixer on medium-high speed, beat cream cheese, lemon zest, salt, and remaining 1/2 cup confectioners’ sugar until light and creamy, 1 to 2 minutes. Add cream and continue to beat on high speed until mixture is light and fluffy and stiff peaks form, 2 to 3 minutes more.

Line an 8 1/2" x 4 1/2" loaf pan with plastic wrap, leaving an overhang on all sides. Line bottom of pan with 3 sheets of graham crackers, breaking ends as needed to fit and using trimmings to fill pan. Spread 1 cup cheesecake mixture on top. Top with 1/2 cup blueberry sauce, then carefully dollop with another 1 cup cheesecake mixture, spreading with an offset spatula or the back of a spoon to avoid the layers merging. Add another layer of graham crackers, then repeat layers of cheesecake, blueberry sauce, and cheesecake; reserve any remaining sauce and cheesecake (cover and refrigerate until ready to use). Top with remaining graham cracker sheets.

Cover pan with plastic wrap and refrigerate at least 4 hours or up to overnight.

Remove top layer of plastic wrap from top of cake. Place a rectangular platter upside down on top of pan, then invert pan. Remove pan and peel off plastic wrap.

Frost top and sides of cake with reserved cheesecake mixture. Top with reserved blueberry sauce.