Pour milk into a bowl and add the 2 boxes of instant pudding.
Whisk until the pudding is well combined and starting to thicken. Chill for a few minutes.
While the pudding chills, layer the bottom of a 9×13-inch pan with a single layer of graham crackers.
Once the pudding is set, take it out of the fridge and fold in the Cool Whip until smooth.
Spread half of the pudding mixture over the graham cracker layer in the pan, spreading evenly.
Add a second layer of graham crackers, followed by the remaining pudding mixture. Top with a third layer of graham crackers.
Slightly melt the lemon frosting in the microwave for about 10 seconds until it’s pourable, then spread it over the final layer of graham crackers.
Chill in the refrigerator for 8 hours before serving.