In a large bowl, whisk together the whole milk and the instant vanilla pudding mix for two minutes. Fold in the thawed frozen topping until everything is well-combined. Editor's Tip: Switch to a rubber spatula when folding in the frozen topping.
In a 13x9-inch baking dish, layer the graham crackers evenly over the bottom. Spread half of the pudding mixture evenly over graham crackers, then repeat the layers once more. Top the pudding mixture with the remaining graham crackers.
Spread the chocolate frosting over the top of the graham crackers. Editor’s Tip: Let the frosting come to room temperature so it’s easy to spread. Otherwise you'll end up dragging and breaking the graham crackers.
Cover the pan tightly with storage wrap, and refrigerate the eclair cake for at least three hours. Once the cake is thoroughly chilled and set, cut the cake into squares and serve.
