Preheat oven to 375 degrees F (190 degrees C). Position rack in center of oven. Butter or spray with a non stick cooking spray 12 - 2 3/4 x 1 1/2 inch muffin cups. Set aside.

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

In another large bowl combine the flours, cocoa powder, brown sugar, baking powder, baking soda, and salt. Stir in the chopped nuts and chocolate chips. 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, using two spoons or an ice cream scoop. Place in the oven and bake until a toothpick inserted in the center of a muffin comes out clean, about 20 - 25 minutes. Transfer to a wire rack and let cool for about 5 minutes before removing from pan. 

Makes 12 regular sized muffins or 6 jumbo muffins.