Preheat oven to 350°F (175°C). Line a 12-cup muffin tin with cupcake liners.
In a large bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
In a separate bowl, whisk together sugar, oil, eggs, and vanilla extract. Gradually add the dry ingredients to the wet ingredients, alternating with buttermilk, beginning and ending with dry ingredients. Mix until just combined.
Stir in hot coffee and crushed Oreos. The batter will be thin.
Fill cupcake liners about 2/3 full.
Bake for 20-22 minutes, or until a wooden skewer inserted into the center comes out clean.
Let cupcakes cool in the tin for a few minutes before transferring to a wire rack to cool completely.
Make Oreo Buttercream: In a large bowl, beat butter until light and fluffy. Gradually add powdered sugar, alternating with milk, until smooth and creamy. Stir in vanilla extract and crushed Oreos.
Frost cooled cupcakes with Oreo buttercream. Garnish with additional Oreo pieces, if desired.
Notes
For best results, use high-quality cocoa powder and fresh ingredients. Store leftover cupcakes in an airtight container at room temperature.