Make the cupcakes: Preheat oven to 350°F (175°C). Line a 12-cup muffin pan with cupcake liners. Place one Oreo cookie at the bottom of each cupcake liner. Set aside.
In a large bowl sift flour, cocoa powder, baking soda and salt. Add sugar, stir and set aside.
In a separate bowl whisk all wet ingredients except coffee/water.
Add dry ingredients to wet ingredients and whisk just until combined. don’t overmix.
Scoop the batter into cupcake liners. Bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool completely.
Make the buttercream: in a large bowl, beat butter until light and fluffy, about 4-5 minutes. Beat in powdered sugar, 1/2 cup at a time, beating in between. Add vanilla extract, milk and beat until incorporated. Add crushed Oreos and fold until combined. Transfer to a piping bag.
frost as desired.
Decorate the cupcakes: top the cupcake with a mini Oreo, whole Oreo cookie or halved Oreo cookie.