01 - Whisk together the instant lemon pudding mixes and cold milk in a large mixing bowl for 2 minutes until mixture thickens.
02 - Beat the heavy cream with powdered sugar and vanilla extract in a separate bowl until stiff peaks form.
03 - Gently fold the whipped cream into the lemon pudding mixture until smooth and fully incorporated.
04 - Arrange a single layer of graham crackers in a 9x13-inch baking dish to completely cover the bottom.
05 - Spread half of the lemon cream mixture evenly over the initial graham cracker layer.
06 - Place another layer of graham crackers over the cream, then spread remaining lemon cream mixture on top.
07 - Finish with a final layer of graham crackers to create the top surface.
08 - Whisk together powdered sugar, lemon juice, milk, and lemon zest until smooth and pourable consistency is achieved.
09 - Pour the lemon glaze evenly over the top graham cracker layer, using a spatula to spread if necessary for complete coverage.
10 - Cover the dish and refrigerate for at least 4 hours, or preferably overnight, to allow the cake to set and crackers to soften properly.
11 - Slice into squares and serve chilled.