Cream together softened butter and both brown and white sugar until smooth
Mash bananas until there are no more clumps, until smooth. Add the bananas into the creamed sugar and butter and add in the 2 eggs and mix until completely combined. Then mix in vanilla.
In a separate bowl, sift together flour, baking soda, salt, and espresso powder.
Gently fold in the dry ingreditants into the wet ingrediants and stir until completely combined. Then fold in the chopped dark chocolate.
Pour batter into a bread load pan and bake for 55 minutes at 350 degrees (F). Once it's baked, let it sit and cool for at least 15 minutes.