01 - Whisk together the instant lemon pudding mixes and cold milk in a large mixing bowl for 2 minutes until mixture thickens considerably.
02 - In a separate bowl, beat the heavy whipping cream with powdered sugar and vanilla extract using an electric mixer or whisk until stiff peaks form.
03 - Gently fold the whipped cream into the prepared lemon pudding mixture until smooth and fully incorporated, taking care not to deflate the cream.
04 - Arrange a single layer of graham crackers in a 9x13-inch baking dish, breaking crackers as needed to cover the bottom completely.
05 - Spread half of the lemon cream mixture evenly over the initial graham cracker layer using an offset spatula.
06 - Top with another layer of graham crackers, then spread the remaining lemon cream mixture evenly across the surface.
07 - Complete the cake with a final layer of graham crackers, ensuring complete coverage.
08 - Whisk together powdered sugar, fresh lemon juice, milk, and grated lemon zest until completely smooth and pourable.
09 - Pour the lemon glaze evenly over the top layer of graham crackers, using a spatula to spread coverage to the edges.
10 - Cover the baking dish with plastic wrap or foil and refrigerate for at least 4 hours, preferably overnight, allowing crackers to soften and flavors to meld.
11 - Cut into squares and serve chilled directly from the refrigerator.