Prep the Oven: Preheat the oven to 350°F (175°C) and line two 12-cup muffin tins with paper liners.
Melt Chocolate Mixture: Heat water, butter, oil, and chocolate in a large saucepan over medium heat until fully melted and smooth.
Mix Dry Ingredients: Whisk flour, sugar, cocoa, baking soda, and salt together in a large bowl.
Combine Wet & Dry: Pour the hot chocolate mixture into the dry ingredients and whisk until blended.
Add Eggs: Whisk in the eggs one at a time until fully incorporated.
Add Buttermilk & Vanilla: Whisk in the buttermilk and vanilla until smooth.
Fill the Liners: Spoon the batter into the muffin cups, filling each about ⅔ full.
Bake: Bake for 17–22 minutes, or until a toothpick inserted into the center comes out clean.
Cool: Cool cupcakes in the tin for 10 minutes before transferring to a rack.