Begin by placing 14 tablespoons of unsalted butter in a medium saucepan over medium heat. Allow it to melt, stirring often. After a few minutes, the butter will start to foam, then turn golden brown and develop a nutty aroma. Remove it from heat and let it cool slightly.
Preheat your oven to 350°F (175°C). Grease your loaf pan with 2 tablespoons of room temperature butter, ensuring it’s well coated.
In a large mixing bowl, whisk together 2 cups of flour, 1 teaspoon of baking powder, 1 teaspoon of baking soda, 1 teaspoon of fine sea salt, and 1 teaspoon of ground nutmeg. Set aside.
In another bowl, combine the browned butter (make sure it’s cooled but still liquid), 1 cup of granulated sugar, and ½ cup of light or dark brown sugar. Mix well until combined. Add in 3 large eggs, 2 teaspoons of pure vanilla extract, and the 4 mashed bananas. Stir until the mixture is smooth.
Gradually add the dry ingredients to the wet ingredients, stirring gently with a rubber spatula until just combined. Be careful not to overmix; a few lumps are perfectly fine.
Sprinkle 1 teaspoon of cinnamon into the batter and fold it in gently. This adds a lovely warmth to the bread.
Pour the batter into your prepared loaf pan, smoothing the top with the spatula. Bake in the preheated oven for 60-70 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, remove the bread from the oven and let it cool in the pan for about 10-15 minutes. Then, transfer it onto a cooling rack to cool completely before slicing.