Preheat your oven to 180°C (fan)/200°C. Line a muffin tray with paper liners.

In a large bowl, combine flour, sugar, cocoa powder, bicarbonate of soda, and a pinch of salt. Whisk until blended.

In a separate bowl, whisk together buttermilk, vegetable oil, eggs, and vanilla extract until smooth.

Pour the wet ingredients into the dry ingredients and stir gently until just combined. Do not overmix.

Fold in the dark chocolate chunks until evenly distributed.

Scoop the batter into the muffin tray, filling each hole about three-quarters full.

Bake in the preheated oven for 20 minutes, checking for doneness with a skewer.

Let the muffins cool in the pan for about 10 minutes before transferring them to a wire rack.