Step 1: Prepare the Pudding Filling

Make the Pudding: In a large bowl, whisk together the lemon pudding mix, cold milk, lemon zest, and vanilla extract until smooth and thickened.

Fold in Cool Whip: Gently fold in the whipped topping until fully combined.

Step 2: Assemble the Cake

Layer Graham Crackers: In a 9x13-inch baking dish, arrange a single layer of graham crackers, breaking pieces as needed to fit.

Add Pudding: Spread half of the lemon pudding mixture evenly over the graham crackers.

Repeat Layers: Add another layer of graham crackers, then spread the remaining pudding mixture on top. Finish with a final layer of graham crackers.

Step 3: Make the Glaze

Whisk Ingredients: In a small bowl, whisk together the powdered sugar, lemon juice, melted butter, and vanilla extract until smooth. Add a teaspoon of milk if needed to thin the glaze.

Spread Over Cake: Pour the glaze evenly over the top layer of graham crackers, spreading it with a spatula.

Step 4: Chill and Serve

Refrigerate: Cover and refrigerate for at least 4-6 hours (preferably overnight) to allow the graham crackers to soften.

Slice and Serve: Garnish with lemon zest or whipped cream if desired. Serve chilled.