Prepare Oven & Pan: Preheat oven to 350 °F (175 °C). Line a 12-cup muffin tin with paper liners.
Mix Dry Ingredients: In a bowl, sift together flour, cocoa powder, baking powder, baking soda, and salt.
Mix Wet Ingredients: In another bowl, whisk buttermilk, oil, eggs, coffee liqueur, and vanilla until combined.
Combine: Gently fold dry ingredients into the wet mixture until just combined. Avoid over-mixing to keep cupcakes soft.
Fill & Bake: Spoon batter into liners, filling each about two-thirds full. Bake for 15–18 minutes, or until a toothpick comes out with a few moist crumbs.
Cool: Transfer cupcakes to a wire rack to cool completely before frosting.
Make Frosting: Beat butter until creamy. Gradually add powdered sugar and cocoa powder, alternating with coffee liqueur. Adjust with cream if needed for consistency.
Frost: Pipe or spread frosting over cooled cupcakes. Garnish with chocolate shavings or festive sprinkles.