01 - Whisk together instant lemon pudding mixes and cold milk in large mixing bowl for 2 minutes until mixture thickens considerably.
02 - Beat heavy cream with powdered sugar and vanilla extract in separate bowl until stiff peaks form and mixture holds its shape.
03 - Gently fold whipped cream into lemon pudding mixture using spatula until smooth and fully incorporated, maintaining airy texture.
04 - Arrange single layer of graham crackers in 9x13-inch baking dish, breaking crackers as necessary to cover bottom completely.
05 - Spread half of lemon cream mixture evenly over graham cracker layer using offset spatula for uniform coverage.
06 - Place another complete layer of graham crackers over cream filling, ensuring full coverage.
07 - Spread remaining lemon cream mixture evenly over second graham cracker layer, smoothing top with spatula.
08 - Arrange final layer of graham crackers over cream, creating solid top surface for glaze application.
09 - Whisk together powdered sugar, fresh lemon juice, milk, and grated lemon zest until smooth and pourable consistency achieved.
10 - Pour lemon glaze evenly over top graham cracker layer, spreading with spatula to cover entire surface.
11 - Cover dish tightly with plastic wrap and refrigerate for minimum 4 hours, preferably overnight, until graham crackers soften completely and cake sets.
12 - Cut into squares and serve chilled directly from refrigerator for best texture and flavor.