Preheat the oven to 350°F (175°C) to ensure even baking.

Grease a 9x9 inch baking pan or line it with parchment paper to prevent sticking.

In a mixing bowl, mash the ripe bananas until smooth.

Add the melted butter, brown sugar, egg, and vanilla extract to the mashed bananas and mix until creamy.

Sprinkle the baking powder, baking soda, salt, and all-purpose flour over the wet mixture and stir gently until just combined.

Fold in the chocolate chips or chopped nuts if using.

Pour the batter into the prepared pan and smooth the top with a spatula.

Bake for 25 to 30 minutes or until a toothpick inserted in the center comes out clean, then let cool in the pan before transferring to a wire rack.