Preheat oven to 350°F and line a muffin tin with cupcake liners.
In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add in the oil, eggs, vanilla, and buttermilk, mixing until smooth.
Carefully stir in the hot water until the batter is combined. It will be thin—that’s okay.
Pour batter into liners, filling each about two-thirds full.
Bake for 18–20 minutes, or until a toothpick inserted in the center comes out clean.
Cool completely before frosting.