Step 1: In a large mixing bowl, combine the two packages of instant vanilla pudding mix with 3 cups of cold whole milk. Whisk the mixture for 2-3 minutes until it begins to thicken. Set aside for a few minutes to allow the pudding to fully set.

Step 2: Once the pudding has thickened, fold in the thawed whipped topping (Cool Whip) until the mixture is smooth and fully combined.

Step 3: In a 9×13-inch baking dish, arrange a single layer of graham crackers on the bottom, breaking the crackers as needed to fit the entire surface. This will be the base of your dessert.

Step 4: Spread half of the pudding and whipped topping mixture over the layer of graham crackers, using a spatula to create an even layer.

Step 5: Place another layer of graham crackers on top of the pudding mixture, then spread the remaining half of the pudding mixture evenly over the graham crackers.

Step 6: Add a final layer of graham crackers over the second layer of pudding. This will create a layered effect that mimics the texture of an éclair.

Step 7: In a medium bowl, prepare the chocolate topping by whisking together the unsweetened cocoa powder, powdered sugar, melted butter, and 1/4 cup of milk. Whisk until smooth and creamy, adding a little more milk if necessary to reach a spreadable consistency.

Step 8: Pour the chocolate topping over the top layer of graham crackers, using a spatula or the back of a spoon to spread it evenly across the surface.

Step 9: Cover the dish with plastic wrap and refrigerate the cake for at least 4 hours, or preferably overnight. This chilling time allows the graham crackers to soften and absorb the flavors of the pudding mixture, creating a cake-like texture.

Step 10: Once fully chilled and set, slice into squares and serve. Enjoy your creamy, chocolatey no-bake dessert!