Place 3 (3.4-ounce) packages instant vanilla pudding and 1 quart whole milk in a large bowl and whisk until smooth.
Add 1 (8-ounce) tub Cool Whip and use a flexible spatula to gently fold together until well combined.
Arrange a layer of graham crackers (about 1 sleeve) in 9x13-inch baking dish, breaking the crackers as needed to fit.
Spread half of the pudding mixture evenly over the graham crackers.
Arrange a second layer of graham crackers on top of the pudding mixture.
Spread the remaining pudding mixture over the top.
Finish with a third layer of graham crackers.
Place 1 cup dark chocolate chips, ¾ cup heavy cream, ¼ cup light corn syrup, and ⅛ teaspoon kosher salt in a medium microwave-safe bowl.
Microwave on HIGH in 15-second increments, stirring after each increment, until the chocolate is melted and the mixture is completely smooth, about 1 minute total.
Pour the chocolate mixture evenly over the top layer of graham crackers.
Smooth it out with the spatula.
Cover the baking dish and refrigerate for at least 8 hours or up to overnight before cutting and serving.
