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, sugar, cocoa powder, baking powder, baking soda, and salt until well combined.

In another bowl, whisk together the buttermilk, vegetable oil, eggs, and vanilla extract until smooth.

Pour the wet ingredients into the dry ingredients and gently fold until just combined. Be careful not to overmix; a few lumps are okay.

Stir in the chocolate chips (and nuts or chocolate chunks if using).

Divide the batter evenly among the muffin cups, filling each about ¾ full.

Bake in the preheated oven for about 18-20 minutes or until a toothpick inserted into the center of a muffin comes out clean or with a few moist crumbs.

Remove the muffins from the oven and let them cool in the tin for a few minutes before transferring them to a wire rack to cool completely.

Enjoy your irresistibly delicious chocolate muffins!