01 - Whisk together the instant lemon pudding mixes and cold milk in a large mixing bowl for 2 minutes until mixture thickens noticeably.
02 - In a separate bowl, beat heavy whipping cream with powdered sugar and vanilla extract using an electric mixer or whisk until stiff peaks form.
03 - Gently fold whipped cream into lemon pudding mixture until smooth and fully incorporated, maintaining light airy texture.
04 - Arrange graham crackers in single layer across bottom of 9x13-inch baking dish, breaking pieces as needed to fit completely.
05 - Spread half of lemon cream mixture evenly over graham cracker base using offset spatula.
06 - Place another complete layer of graham crackers over cream filling.
07 - Spread remaining lemon cream mixture evenly across second cracker layer.
08 - Top with final layer of graham crackers, creating even surface for glaze.
09 - Whisk powdered sugar, fresh lemon juice, milk, and grated lemon zest until smooth and pourable consistency forms.
10 - Pour lemon glaze evenly over top graham cracker layer, spreading gently with spatula to cover completely.
11 - Cover dish with plastic wrap and refrigerate minimum 4 hours or overnight to allow flavors meld and crackers soften completely.
12 - Slice into squares and serve cold directly from refrigerator.