Prep the pan and oven: Line a 12-cup muffin tin with paper liners. Preheat your oven to 350°F (175°C).
Mix dry ingredients: In a large bowl, whisk 1 cup (125g) all-purpose flour, 1/2 cup (45g) unsweetened cocoa powder, 3/4 cup (150g) granulated sugar, 1 teaspoon baking powder, 1/2 teaspoon baking soda, and 1/2 teaspoon fine salt until no cocoa lumps remain.
Combine wet ingredients: In a separate bowl or large measuring cup, whisk 1 large egg, 1/2 cup (120ml) buttermilk, 1/3 cup (80ml) neutral oil, and 1 teaspoon vanilla extract until smooth.
Bring in the heat: Pour 1/2 cup (120ml) hot coffee or hot water into the wet mixture and whisk.
The batter will look thin—that’s good. Hot liquid helps bloom the cocoa for deeper flavor.
Make the batter: Pour the wet ingredients into the dry ingredients. Whisk gently just until combined. Do not overmix.
A few small lumps are fine.
Fill the liners: Divide the batter evenly among the 12 liners, filling each about two-thirds full. If using chocolate chips, sprinkle a few into each cup now.
Bake: Bake for 16–20 minutes, or until the tops spring back when lightly pressed and a toothpick comes out with a few moist crumbs (not wet batter).
Cool: Let cupcakes cool in the pan for 5 minutes, then transfer to a wire rack to cool completely before frosting.
Optional frosting: Beat 1/2 cup (115g) softened unsalted butter until creamy. Sift in 1 1/2 cups (180g) powdered sugar and 1/4 cup (20g) cocoa powder.
Add 1 teaspoon vanilla, a pinch of salt, and 1–2 tablespoons milk or cream. Beat until fluffy and spreadable. Adjust sweetness or thickness as needed.
Frost and serve: Swirl or pipe frosting onto cooled cupcakes.
Finish with sprinkles, a dusting of cocoa, or a pinch of flaky salt.