Preheat the oven to 350°F and prepare a cupcake pan or two with liners. This recipe makes around 16 cupcakes.
In a small bowl, whisk the cocoa powder and boiling water together until it is smooth and the cocoa is dissolved. Let it cool down.
In a large mixing bowl, beat the oil, granulated sugar, brown sugar, and eggs together until creamy and smooth. Then whisk in the cocoa mixture and vanilla. This is your bowl of wet ingredients.
Combine the flour, baking soda, baking powder, and salt in a separate bowl. Alternate whisking in the the flour, buttermilk, and then the remaining flour into your wet ingredients. Fold everything together until the flour is just combined.
Add a spoonful of batter into the bottom of each prepared cupcake tin to cover the bottom. Then, place an Oreo cookie on top, and then top it off with more batter until the tins are ¾ full.
Bake for 18-20 minutes, or until the cupcakes are set. The top of the cupcake should spring back when you gently tap it. Let the cupcakes cool completely before frosting.