Preheat oven to 350°F (175°C) and grease an 8x8-inch square baking pan with butter or line with parchment paper.

In a large mixing bowl, whisk together the melted butter and brown sugar until smooth and well combined.

Add the egg and vanilla extract to the butter mixture and whisk vigorously until the texture is glossy.

Stir in the mashed bananas until evenly incorporated.

Sift the flour and salt into the wet ingredients, then fold gently with a spatula until just combined, ensuring no dry flour pockets remain.

Fold in the chocolate chips.

Pour the batter into the prepared pan and spread evenly with a spatula.

Bake for 25 to 30 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out clean.

Remove from oven and let cool completely in the pan on a wire rack before slicing into 16 squares.