Preheat oven to 200°C fan/220°C, Line a muffin tray with muffin liners.
Melt butter in the microwave. Set aside,
In a large mixing bowl sift flour, cocoa powder, sugar, baking powder, baking soda and salt. Mix in salt and three-quarters of the chocolate chunks. Set aside.
To a jug, add buttermilk, oil, melted butter, eggs and vanilla extract. Whisk to combine.
Make a hole in the centre of the dry ingredients, and pour the wet ingredients into the dry ingredients. Fold the wet ingredients into the dry ingredients until combined.
Scoop the batter into the muffin liners, filling them to the top. Bake for 5 minutes at 200°C fan/220°C, then reduce the oven temperature to 160°C fan/180°C, Bake for an additional 15 minutes or until a toothpick inserted in the centre comes out clean.
Leave the muffins to cool in the pan on a cooling rack for 10 minutes, then transfer them to the cooling rack to cool complety.
