Step 1: Prepare the Baking Dish

1. Preheat your oven to 350°F (175°C).
2. Line an 8×8-inch baking dish with parchment paper or lightly grease it with butter or non-stick spray.

Step 2: Mix the Wet Ingredients

1. In a large mixing bowl, combine the melted butter, granulated sugar, and brown sugar. Whisk until smooth and creamy.
2. Add the egg and vanilla extract, mixing until fully incorporated.
3. Stir in the mashed bananas until well combined.

Step 3: Combine the Dry Ingredients

1. In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon (if using).
2. Gradually add the dry ingredients to the wet ingredients, mixing gently until just combined. Avoid overmixing to keep the bars tender.

Step 4: Add the Chocolate Chips

1. Fold in the chocolate chips and any optional add-ins, like nuts or coconut. Reserve a handful of chocolate chips to sprinkle on top.

Step 5: Bake the Bars

1. Pour the batter into the prepared baking dish and spread it evenly with a spatula.
2. Sprinkle the reserved chocolate chips on top for an extra chocolatey finish.
3. Bake in the preheated oven for 25–30 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.

Step 6: Cool and Serve

1. Allow the bars to cool completely in the pan before lifting them out using the parchment paper.
2. Slice into 16 squares and serve. Enjoy warm or at room temperature!