3 1/2 cups whole milk
2 boxes (3.4 ounces each) instant French vanilla pudding mix
16 ounce tub Cool Whip (this is 1 large tub, or use small 8-ounce tubs) thawed
1 box graham crackers
1 tub chocolate frosting
In a large mixing bowl, whisk together the milk and instant vanilla pudding until well combined. Set aside to thicken for a few minutes, stirring occasionally. Once thickened, fold in the Cool Whip.
Place a single layer of graham crackers in the bottom of a 9×13-inch pan. Top with half of the pudding mixture. Add another single layer of graham crackers, then the remaining pudding mixture. Top with a final layer of graham crackers.
Scoop the chocolate frosting into a microwave-safe bowl and heat in 15-second increments until melted, stirring well between each cooking interval. Pour the frosting over top of the eclair cake.
Refrigerate the eclair cake for about 30 minutes until the chocolate frosting is set, then cover with plastic wrap and chill overnight, or 8 hours.
Slice the eclair cake into 12 servings and serve chilled.