Preheat the oven to 350°F.

Line 24 muffin tin cups and place an Oreo in each one.

Combine cake mix, pudding mix, sour cream, vegetable oil, eggs, milk, and vanilla extract together in a large bowl, mixing until just combined.

Add chocolate chips and mix again, until well distributed.

Scoop cake batter over the Oreos, only filling each cup to be about 2/3 of the way full.

Bake for 20 minutes.

Meanwhile, use a stand mixer to whisk together the butter and shortening. Add the powdered sugar and milk, alternating 1 cup of powdered sugar with 1 tablespoon of milk and whisking in between each addition until smooth. Whisk in the vanilla.

Hand crumble 15 Oreos into the butter cream. Use a spatula to mix in well.

Once the cupcakes have cooled, spread the Oreo butter cream on top. Crumble another Oreo on top of the butter cream (you could easily spread one Oreo over two cupcakes).