Preheat oven to 375 degrees F (190 degrees C). Position rack in centre of oven. Butter or line with paper 12 - 2 3/4 x 1 1/2 inch muffin cups.

In a large measuring cup or bowl whisk together the melted butter, eggs, buttermilk, and vanilla extract.

In another large bowl whisk together the flour, cocoa powder, sugar, baking powder, baking soda, and salt.

With a rubber spatula fold the wet ingredients into the dry ingredients and stir only until the ingredients are combined. Do not over mix the batter or tough muffins will result.

Evenly fill the muffin cups with the batter (the muffin cups will be full), using two spoons or an ice cream scoop. Place in the oven and bake until a toothpick inserted in the centre of a muffin comes out clean, about 20 minutes. Transfer to a wire rack and let cool for about 5 minutes before removing from pan.