Preheat oven to 400 degrees and line a 12-cup (standard) muffin tin with paper liners or spray with non-stick spray.
In a large bowl, whisk together the gluten free flour, cocoa powder, xanthan gum, granulated sugar, baking powder, baking soda, and salt. Stir in the chocolate chips and then set the bowl aside.
In a medium bowl, whisk together the eggs, buttermilk, coffee, oil, and vanilla extract. Pour the wet ingredients into the dry ingredients and stir until combined.
Transfer the batter to the prepared muffin cups, dividing the batter evenly.
Bake the muffins at 400 degrees for 15-18 minutes or until done. Cool the muffins in the pan for 5 minutes and then remove them from the pan to cool completely on a wire rack.
To make this recipe dairy free, use 1/2 cup unsweetened coconut milk beverage (or dairy free milk of choice) plus 1 1/2 teaspoons white vinegar in place of the buttermilk.
Store leftovers at room temperature in an air-tight container up to 3 days. These muffins also freeze well in a freezer bag. Defrost at room temperature or in the microwave.