Preheat oven to 350°F. Place the oven rack in the middle of the oven. Grease and flour a 9x13 inch pan. Set aside.
In the bowl of a stand mixer whisk the cake flour, sugar, cocoa powder, baking soda, and salt.
In a separate bowl, or large liquid measuring cup, whisk the vegetable oil, sour cream, buttermilk, egg, vanilla extract, and white vinegar. Add the wet ingredients to the dry ingredients (using a paddle attachment) and mix on low until ingredients are combined.
Pour the batter into the prepared pan and bake in the oven for 23-26 minutes or until a toothpick inserted in the center comes out with a few moist crumbs on it. (Do your best not to overbake the cake, as that will result in a drier texture). Remove from the oven and let cool on a wire rack for 10 minutes.
Use a wooden skewer, straw, or back of a wooden spoon and poke holes all over the cake, leaving about ½” between each hole. Drizzle the sweetened condensed milk over the entire cake. Cover and chill in the fridge for 2 hours. In a large bowl (or the bowl of a stand mixer fitted with whisk attachment) add the dry Oreo instant pudding mix, heavy cream, powdered sugar, milk (I used 2%) vanilla extract. Using a hand mixer, mix until smooth and thickened, about 1-2 minutes on medium speed.
Spread the mousse over the cake then sprinkle the chopped Oreos overtop. Store in the fridge until ready to serve.