Preheat your oven to 350°F (180°C) and line a 12-cup muffin pan with paper liners.
In a large bowl, whisk together the 1 cup (125g) all-purpose flour, 1/2 cup (45g) unsweetened cocoa powder, 3/4 teaspoon baking soda, 1/2 teaspoon baking powder, 1/4 teaspoon salt, and 1 cup (200g) granulated sugar.
In another large bowl, whisk the 1/4 cup (60ml) vegetable oil, 1 large egg, 1 teaspoon vanilla extract, and 1/2 cup (120ml) buttermilk until the mixture is smooth and no pieces of egg remain.
Make a well in the center of the dry ingredients, then pour in the wet mixture. Gently whisk to combine.
When the batter is about 60–70% mixed, carefully stir in the 1/3 cup (80ml) freshly brewed coffee (or boiling water) and whisk until completely smooth.
Divide the batter among the prepared muffin cups, filling each about halfway. You should get 11–12 cupcakes; if you only fill 9–10 cupcakes, the cavities are too full.
Bake one tray at a time on the middle rack for 16–20 minutes, or until the tops are slightly firm and a toothpick inserted in the center comes out clean.
Let the cupcakes cool in the pan for 10–20 minutes, then transfer to a wire rack to cool completely before icing, about 60 minutes.