In a large bowl, mix together the eggs, white sugar and butter until smooth. Stir in the buttermilk and coffee. The mixture will look curdled. Combine the flour and baking soda; stir into the coffee mixture. Blend in bran cereal. Cover and refrigerate for at least 20 minutes or up to a week.
Preheat the oven to 375 degrees F (190 degrees C). Grease a muffin pan or line with paper muffin liners. Fill each cup with 1/4 cup batter.
Bake for 18 to 20 minutes in the preheated oven, or until the top springs back when lightly touched. Cool in pan before removing.