01 - Whisk together instant lemon pudding mixes and cold milk in large mixing bowl for 2 minutes until mixture thickens completely.
02 - In separate bowl, beat heavy cream with powdered sugar and vanilla extract using electric mixer until stiff peaks form.
03 - Gently fold whipped cream into lemon pudding mixture until smooth and fully incorporated, maintaining airy texture.
04 - Arrange single layer of graham crackers in 9x13-inch baking dish, breaking crackers as needed to cover bottom completely.
05 - Spread half of lemon cream mixture evenly over graham cracker layer using spatula.
06 - Top with another layer of graham crackers, then spread remaining lemon cream mixture over crackers.
07 - Arrange final layer of graham crackers over cream filling, ensuring complete coverage.
08 - Whisk together powdered sugar, lemon juice, milk, and lemon zest in small bowl until smooth and pourable consistency achieved.
09 - Pour lemon glaze evenly over top layer of graham crackers, spreading with spatula to cover entire surface.
10 - Cover dish with plastic wrap and refrigerate for minimum 4 hours or overnight to allow cake to set and graham crackers to soften properly.
11 - Cut into squares and serve chilled directly from refrigerator.