Preheat your oven to 350 degrees. Line a 12 count muffin tin with paper liners or spray to coat well with cooking spray.
In the top of a double boiler, melt the chocolate and espresso powder. Remove from heat and let cool. If you dont have a double boiler, this step can be done in the microwave by melting the chocolate for 5 seconds at a time, stopping to stir in between, until the chocolate is fully melted.
In a large bowl, whisk together the flour, sugar, baking soda, salt, and cinnamon. In a separate medium size bowl, whisk together the eggs, banana, oil, buttermilk, molasses, and vanilla.
Add the wet ingredients into the dry ingredients, stirring just until combined. Spoon the batter evenly into the prepared muffin tins. Using the back of a spoon, make a shallow hole in the middle of each muffin and place a dollop of the chocolate espresso mixture into each of them evenly. You can put as much or as little of the chocolate as you like depending on your taste.
Using a toothpick, swirl the chocolate mixture into the muffin mixture.
Bake until a wooden pick inserted in the center of a muffin comes out clean. 15 minutes. Let the muffins cool in the pan for about 5 minutes before removing. Serve warm or at room temperature.