Preheat oven to 220C/425F degrees. Line the muffin tin with 12 paper cups.

Melt the butter in a bowl, and set aside to cool.

In a medium sized bowl, sift together the all purpose flour, unsweetened cocoa powder, baking powder, baking soda, salt and granulated sugar.

In a separate bowl, whisk together the eggs with the buttermilk, oil, melted butter, coffee granules and vanilla extract. Pour this mixture into the dry ingredients and mix until just combined. Do not over mix. The batter will be thick and lumpy.

Gently fold in the chocolate chips.

Divide the mixture between the muffin cups and fill them almost all the way to the top. Bake for 3 minutes and then reduce the oven temperature to 180C/350F - the high temperature helps the muffins rise high. Bake for an additional 12-17 minutes (15-20 minutes total), until a toothpick inserted into the center of the muffin comes out clean - NOTE: you will have to be careful as there are so many chocolate chips you may get a melty pocket and it may seem the muffins aren't cooked through - either insert the toothpick avoiding the chocolate chips or use the touch and spring method - if the muffins are cooked they'll spring back when you touch the top. Transfer to a wire rack and let cool for about 15 minutes before removing from pan.