01 - Whisk together instant lemon pudding mixes and cold milk in a large mixing bowl for 2 minutes until mixture thickens significantly.
02 - In a separate bowl, beat heavy whipping cream with powdered sugar and vanilla extract until stiff peaks form, approximately 3-4 minutes.
03 - Gently fold whipped cream into lemon pudding mixture using a rubber spatula until completely smooth and no white streaks remain.
04 - Arrange whole graham crackers in a single layer across the bottom of a 9x13-inch baking dish, breaking pieces as needed to cover completely.
05 - Spread half of the lemon cream filling evenly over the graham cracker base using an offset spatula.
06 - Place another layer of graham crackers over the cream filling, ensuring complete coverage.
07 - Spread remaining lemon cream mixture evenly over the middle graham cracker layer.
08 - Finish with a final layer of graham crackers on top, creating a smooth surface for the glaze.
09 - Whisk together powdered sugar, fresh lemon juice, milk, and grated lemon zest in a small bowl until completely smooth and pourable.
10 - Pour lemon glaze evenly over the top layer of graham crackers, spreading gently with a spatula to cover entire surface.
11 - Cover baking dish tightly with plastic wrap and refrigerate for at least 4 hours or preferably overnight to allow flavors to meld and crackers to soften completely.
12 - Cut into 12 equal squares and serve chilled directly from the refrigerator.