01 - Whisk together instant lemon pudding mixes and cold milk in a large mixing bowl for 2 minutes until mixture thickens completely.
02 - Beat heavy whipping cream with powdered sugar and vanilla extract in a separate bowl until stiff peaks form.
03 - Gently fold whipped cream into lemon pudding mixture until smooth and fully incorporated.
04 - Arrange graham crackers in a single layer across the bottom of a 9x13-inch baking dish, breaking crackers as needed to fit.
05 - Spread half of the lemon cream mixture evenly over the graham cracker layer.
06 - Place another layer of graham crackers over the cream, then spread remaining lemon cream mixture on top.
07 - Arrange final layer of graham crackers over the cream filling.
08 - Whisk powdered sugar, lemon juice, milk, and lemon zest together until smooth and pourable consistency is achieved.
09 - Pour lemon glaze evenly over top layer of graham crackers, spreading with spatula to cover completely.
10 - Cover dish and refrigerate for at least 4 hours, preferably overnight, allowing crackers to soften and flavors to meld.
11 - Cut into squares and serve cold directly from the refrigerator.