In a large bowl, whisk together the instant lemon pudding mix and cold milk. You want to ensure that the mixture is smooth and well combined. It should thicken nicely after a minute or two of whisking. Watch for any lumps, and if you see any, whisk them out until you have a creamy consistency.
Gently stir in the lemon zest and half of the Cool Whip. This is where you infuse that bright, citrusy flavor into your pudding mix. Use a folding motion to combine, being careful not to deflate the whipped topping too much. You want to maintain that light texture.
Spread a small amount of the pudding mixture in the bottom of a 9x13-inch pan. This initial layer helps keep the graham crackers from sliding around when you top them with the pudding.
Place a single layer of graham crackers in the bottom of the pan, breaking pieces as necessary to cover the entire base. The crackers will provide the structure for your cake.
Spread half of the lemon pudding mixture on top of the graham crackers. Make sure to cover them evenly, allowing the filling to seep into the cracks. This step helps the layers bond nicely.
Do a second layer of graham crackers on top of the pudding. Again, break the pieces as needed for a complete layer. The layers will create a delightful texture in every bite.
Repeat with the remaining lemon pudding mixture, spreading it evenly over the second layer of crackers. Then, add a final layer of graham crackers on top, ensuring it’s well covered.
Spread the remaining Cool Whip on top of the last layer of graham crackers. This will be the delightful, fluffy topping that gives your cake an appealing finish.
Cover the pan and refrigerate for at least 2 hours before serving. This resting time allows the flavors to meld and the cake to firm up, making it easier to slice and serve.
When ready to serve, garnish with fresh raspberries or blackberries if desired. This adds a beautiful touch and a burst of flavor that complements the cake wonderfully.
