Preheat oven to 350°F (175°C) and grease the loaf pan with cooking spray.

Melt unsalted butter in a sauté pan over medium heat until golden and fragrant, about 5–7 minutes. Let cool slightly.

Mash bananas in a bowl, then mix in eggs until combined.

In another bowl, whisk together flour, brown sugar, baking powder, cinnamon, salt, and nutmeg.

Combine banana-egg mixture with dry ingredients and fold in brown butter until just mixed.

Transfer batter to the prepared pan, place halved banana on top, and sprinkle with brown sugar.

Bake for 70 to 80 minutes until a toothpick inserted in the center comes out clean.

Let cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.