Preheat and prepare pan. Preheat the oven to 350° F (180°C). Line one cupcake pan with paper liners by alternating them in the pan. Set aside.
Combine dry ingredients. In a mixing bowl, whisk together the flour, cocoa powder, baking powder, baking soda and salt and set aside. 6 tablespoons (45 g) all purpose flour ¼ cup (21 g) unsweetened cocoa powder ½ teaspoon baking powder ¼ teaspoon baking soda ¼ teaspoon salt
Combine wet ingredients. In a second mixing bowl, whisk together egg, sugar, vanilla extract, oil, and buttermilk. 1 large egg 6 tablespoons granulated white sugar 1 teaspoon vanilla extract ¼ cup (60 mL) neutral-tasting oil (I used avocado) ¼ cup (60 ml) buttermilk
Add the dry ingredients. Add the dry ingredients to the wet ingredient mixture, mixing just until combined. Do not overmix.
Bake. Divide the batter between the prepared paper liners, filling each about 2/3 full. Bake 15-20 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool in pan for 5 minutes, then transfer to a cooling rack to cool completely. Store leftover cupcakes, covered at room temperature or in the refrigerator for 3 days. You can also freeze frosted or unfrosted cupcakes up to 2-3 months. Thaw overnight in the refrigerator before enjoying.