Whisk the instant chocolate pudding and milk together in a bowl until smooth and free of lumps. Refrigerate while preparing the remaining layers so it can fully set.

Preheat oven to 350°F. Combine crushed Oreos and melted butter until evenly moistened. Press firmly into the bottom of an ungreased 9×13 pan to form an even crust. Bake for 10 minutes, then transfer to a cooling rack to cool completely.

To make the ganache, heat the heavy cream in a saucepan over medium heat until it just begins to simmer, with bubbles forming around the edges. Pour the hot cream over the chopped chocolate in a bowl. Let sit for 5 minutes, then stir slowly until smooth and glossy.

Pour the ganache over the cooled Oreo crust and spread evenly with an offset spatula. Allow the ganache to fully cool and set before adding the next layer. You can refrigerate the pan for 20 minutes to speed this up.

In a large bowl, beat the heavy cream, powdered sugar, and vanilla extract until stiff peaks form. Refrigerate the whipped cream until ready to use.

In another bowl, beat the softened cream cheese, powdered sugar, and vanilla extract until smooth and creamy. Gently fold in 1½ cups of the prepared whipped cream until light and fully combined. Spread this mixture evenly over the cooled ganache layer.

Fold crushed Oreos into the chilled pudding until evenly distributed. Gently spread the pudding layer over the cream cheese layer.

Spread the remaining whipped cream evenly over the top. Garnish with crushed Oreos. Refrigerate until fully set before slicing and serving.