Preheat the oven to 350°F and grease a 9x13-inch baking pan with nonstick spray and set aside.
In a large bowl or stand mixer fitted with a whisk attachment, mix together the cake mix, chocolate pudding mix, eggs, sour cream, vegetable oil, ½ cup milk, salt, and vanilla.
Pour the batter into the prepared baking pan and bake for 30 to 35 minutes until a toothpick or cake tester inserted into the cetner comes out clean.
Remove from oven and allow to cool completely in the pan and poke holes all over the cake with the handle of a wooden spoon.
Filling
Prepare the pudding mix by whisking together the mix and 2 cups of cold milk in a medium bowl until smooth.
Spread the prepared pudding over the top of the cooled cake and refrigerate for 1 hour.
Frosting
In a large bowl or stand mixer fitted with a paddle attachment, whip the heavy cream, ⅓ cup dry pudding mix, and powdered sugar on medium-high speed until light and fluffy, about 3 to 4 minutes.
Spread out over the cake, then sprinkle the crushed Oreos over the top of the frosting.
Notes
Want less cream and more chocolate? Substitute the filling for a chocolate pudding or ganache instead.
Make a golden version with yellow cake and golden Oreos.
You can also skip the frosting and top with an 8 oz. tub of thawed cool whip.