Pour 3-1/2 cups milk into a large bowl. Add both 3.4-ounce boxes of French vanilla (or regular vanilla) instant pudding and whisk briskly until completely smooth and lump-free, about 2–3 minutes. (You may use a hand mixer if you prefer.)

Use a spatula to gently fold in the completely thawed 8-ounce package of frozen whipped topping until the pudding mixture is well incorporated. Set the pudding mixture aside.

Lightly spray a 9×13-inch pan with cooking spray.

Arrange honey graham crackers in a single layer to fully cover the bottom of the pan. Break crackers as needed to cover the entire surface.

Spoon half of the pudding mixture over the graham crackers in dollops. Use the back of a spoon or a spatula to gently spread into an even layer, taking care not to slide the crackers.

Place a second full layer of graham crackers over the pudding, covering the surface.

Spoon the remaining pudding mixture over the second graham cracker layer and gently spread into an even layer.

Add the final layer of graham crackers on top, covering the pudding completely.

Place the pan in the refrigerator while you prepare the chocolate ganache.

In a medium microwave-safe bowl combine 1-1/4 cups milk chocolate chips, 2/3 cup heavy cream, and 1 tablespoon unsalted butter. Microwave for 30 seconds, then stir for about 20 seconds. Continue microwaving in 15-second bursts, stirring 15–20 seconds after each burst, until the mixture is completely melted and smooth.

Let the ganache stand at room temperature for about 5 minutes to cool slightly, then pour it over the top layer of graham crackers and gently spread to cover evenly.

Cover the pan and chill in the refrigerator for at least 8 hours or overnight so the pudding sets and the graham crackers soften into a cake-like texture.

When ready to serve, let the cake stand at room temperature for about 5 minutes. Use a hot, sharp knife (run under hot water and dry between cuts) to slice cleanly, and a metal spatula to lift bars. Store any leftovers covered tightly in the refrigerator.