Preheat oven to 425ºF/218ºC. Line 12 muffin cups with liner papers or grease well.
In a large bowl combine together sifted flour, cocoa, instant coffee powder, baking powder, baking soda, sugar and salt. Set aside.
In a medium bowl, whisk the eggs with the buttermilk, oil/melted butter, coffee granules and vanilla extract until combined. Pour the wet ingredients into the dry ingredients and mix with a rubber spatula or a wooden spoon until just combined. Do not over mix. The batter should be thick. Add in chocolate chips or chunks and fold gently.
Divide batter evenly between muffin cups, almost all the way to the top (Tips: you can use the ice cream scoop to scoop out the batter). Sprinkle more chocolate chips as desired. Bake for 5 minutes and then reduce the oven temperature to 350ºF/175ºC. Continue to bake for an additional 14-15 minutes (19-20 minutes total), until a toothpick inserted into the center of the muffin comes out clean. Remove from the oven. Allow to cool for 10 minutes in the pan before transferring to a wire rack to cool completely.
Muffins can be kept in an airtight container in the fridge for up to 3 days and stays frozen for up to 2 months. Serve them at room temperature. Thaw overnight and reheat before serving.