Preheat oven to 350 degrees F. Line muffin tin with paper liners or spray with non-stick cooking spray. Place 1 whole Oreo in the bottom of each muffin liner.

In the bowl of a stand mixer, fitted with the paddle attachment, or with a hand mixer in a large bowl, beat together the cake and pudding mixes, sour cream, oil, eggs, vanilla and water mixture. Beat for about two minutes on medium speed until well combined.

Using a large cookie scoop, fill each muffin cup 2/3 of the way full.

Bake in preheated oven for 16-20 minutes or until the tops of the cakes spring back when lightly touched. Allow cupcakes to cool inside muffin tins for about 10 minutes.

Remove cupcakes from muffin tins and allow to fully cool on a wire rack. Once cupcakes are cool, prepare your frosting.

In the bowl of an electric mixer fitted with the paddle attachment, whip butter for 5 minutes on medium speed (I use "4" on my KitchenAid). Butter will become pale & creamy.

Add the powdered sugar, milk, and vanilla extract. Mix on low speed for 1 minute, and then on medium speed for 5 minutes. Add in crushed Oreos and mix to incorporate completely, about 1 minute.

Frost cooled cupcakes immediately. If desired, top with half an Oreo or a mini Oreo to garnish.