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.

Place all of the dry ingredients into the bowl of a stand mixer and stir on low for 30 seconds to fully combine them.

Add the vegetable oil, eggs, vanilla, and buttermilk and mix on low until just combined.

With the mixer still on low, add the hot coffee (or hot water) in a slow stream, then turn the mixer to medium and beat until smooth, about 2 minutes. The batter will be very thin.

Pour into prepared cake pans no more than ⅔ full and bake for 32-36 minutes, until a wooden toothpick inserted comes out clean. Cool completely.

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

In the bowl of a stand mixer fitted with the paddle attachment, cream the butter on medium-high speed until it's creamy and pale in color, about 5 minutes.

Add the powdered sugar a few cups at a time, mixing on low speed and scraping down bowl and paddle in between intervals.

Keep the mixer on low speed and add the vanilla, milk, and salt. Mix until fully incorporated and uniform, 1-2 minutes.

Mix in the Oreo cookie crumbs on low speed until uniform and well-dispersed.

Once the black velvet cake layers are completely cooled, level them to your desired height.

Add a swipe of cookies and cream buttercream onto a cardboard cake circle and place the first cake layer on top.

Fill and stack the cake with cookies and cream buttercream, then crumb coat the cake.

Refrigerate the cake for 15-20 minutes to let the crumb coat firm up before frosting the cake with the rest of the cookies and cream buttercream.

Frost a smooth buttercream finish onto the cake.

Reserve 8 Oreo cookies for the top of the cake, then chop the rest into pieces of various size and shape.

Press the chopped cookies onto the bottom third of the cake in a mosaic pattern.

Place the remaining cookies & cream buttercream into a piping bag fitted with Wilton Tip 1M and pipe swirls around the top of the cake, spaced about ¼ inch apart.

Place an Oreo cookie in between each swirl.