Preheat oven to 350°F (175°C). Line a 12-cup muffin tin with cupcake liners.
In a large bowl, whisk flour, sugar, cocoa, baking soda, baking powder, and salt.
Add buttermilk, warm water, oil, egg, and vanilla. Whisk until smooth and lump-free.
Divide batter evenly into liners, filling about 2/3 full. Bake 18–20 min or until a toothpick comes out clean. Cool completely.
Make the frosting: Beat butter until creamy. Gradually add powdered sugar, vanilla, and cream. Beat until light and fluffy.
Pipe frosting onto cooled cupcakes using a large round or star tip.
Make the ganache: Heat cream until steaming, then pour over chocolate chips. Let sit 2 min, then stir until glossy.
Let ganache cool 10–15 minutes. Drizzle over frosting with a spoon or use a squeeze bottle for perfect drips.