Step 1: Preheat your oven to 350°F (175°C).
Step 2: Line your cupcake pan with parchment liners.
Step 3: In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking soda, and salt.
Step 4: In another bowl, combine the melted butter, vegetable oil, water, egg, buttermilk, and vanilla extract. Whisk until well blended.
Step 5: Pour the wet mixture into the dry ingredients and gently fold together until just combined.
Step 6: Fill each cupcake liner about two-thirds full with the batter.
Step 7: Bake for 18-20 minutes or until a toothpick comes out clean.
Step 8: Cool in the pan for 5 minutes, then transfer to a cooling rack.