In a large mixing bowl, beat the cream cheese, powdered sugar, and cocoa powder until smooth and fluffy.
Gently fold in the Cool Whip until fully combined.
Arrange a single layer of chocolate graham crackers in the bottom of an 8×8-inch or 9×9-inch baking dish.
Spread 1/3 of the cream cheese mixture evenly over the graham crackers.
Repeat the layers 2 more times.
To make the ganache, combine the heavy whipping cream and chocolate chips in a microwave-safe bowl. Microwave in 30-second intervals, stirring after each interval, until melted and smooth.
Pour the ganache evenly over the cake.
Refrigerate for 4–5 hours, or overnight, until the graham crackers have softened.
Top with mini chocolate chips, if desired, before serving.