Preheat your oven to 350°F (175°C) and lightly coat an 8 or 9-inch square baking pan with nonstick spray or parchment paper.

In a large mixing bowl, combine melted unsalted butter and brown sugar. Beat until smooth and well blended, about 2-3 minutes. Add in the eggs and vanilla extract, mixing until fully incorporated.

Mash the very ripe bananas in a separate bowl and fold them into the wet mixture until combined.

Whisk together the all-purpose flour, baking soda, and salt in another bowl until evenly distributed.

Gradually add the dry ingredients to the wet mixture, folding gently until just combined. If using pecans, fold them in at this stage.

Pour the batter into the prepared pan, smooth the top, and sprinkle granulated sugar on top before baking.

Bake for 45-50 minutes, checking for doneness with a toothpick.

Allow the cake to cool in the pan for 10-15 minutes, then transfer to a wire rack to cool completely before slicing.