Preheat your oven to 350°F (175°C).
Line a muffin tin with paper liners or grease it lightly.
In a large bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.
In a separate bowl, beat the eggs and then add the sugar, vanilla extract, and vegetable oil.
Gradually mix in the buttermilk into the wet ingredients until combined.
Fold the wet ingredients into the dry ingredients until just combined, avoiding overmixing.
If using, fold in chocolate chips until evenly distributed.
Scoop the batter into the prepared muffin tin, filling each cup about ¾ full.
Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Allow to cool in the tin for about 5 minutes before transferring to a wire rack.
