Preheat oven to 175°C (350°F) and line a 12-hole cupcake pan with cases.
Melt the butter and add to a stand mixer bowl fitted with the paddle attachment.
Add oil, coffee, buttermilk, egg, and vanilla, mixing to combine.
In another bowl, whisk together flour, sugar, cocoa powder, baking soda, and salt.
With the mixer on low, gradually add the dry ingredients to the wet, pausing to scrape down the bowl.
Scoop about 3 tbsp of batter into each cupcake liner. Bake for 20–22 minutes, or until a toothpick comes out clean. Cool completely on a wire rack.