Preheat the oven to 350ºF (177ºC) and prepare three 6-inch or two 8-inch cake pans by spraying the sides with cooking spray and fitting the bottoms with a wax paper or parchment cake circle.

Roughly chop the Oreos into pieces that are about ¼ inch. Set aside.

Add the sifted cake flour, baking powder, baking soda, and salt into a bowl and whisk to combine. Set aside.

In the bowl of your stand mixer fitted with the paddle attachment, cream the butter on high for two minutes. Add the sugar and vegetable oil and continue to mix on high for another two minutes.

Add the eggs one at a time, mixing thoroughly after each addition. Add the vanilla and sour cream and mix for one minute on high speed.

Turn the mixer off and add the dry ingredients all at once. Mix on low speed until just combined, then add the milk slowly and mix until just incorporated. Fold in the chopped Oreo cookies.

Pour the batter into the prepared cake pans and bake for 30-35 minutes, until a toothpick inserted comes out clean. Cool the cakes in the pan for five minutes before removing and continuing to cool on a wire rack.

Place the Oreo cookies into a food processor and grind them into fine crumbs.

In the bowl of a stand mixer, cream the butter on medium-high speed until creamy and pale in color, about 5 minutes.

Add the powdered sugar a few cups at a time, mixing on low speed. Add the vanilla, milk, and salt. Mix until fully incorporated.

Mix in the Oreo cookie crumbs on low speed until uniform.

Once the cake layers are completely cooled, level them to your desired height. Add a swipe of Oreo buttercream onto a cardboard cake circle and place the first cake layer on top.

Fill and stack the cake with Oreo buttercream, then crumb coat the cake. Refrigerate for 15-20 minutes.

Frost the cake with Oreo buttercream and use a scalloped cake comb to create a grooved texture on the sides. Pipe swirls around the top of the cake and place an Oreo cookie in between each swirl.