Preheat your oven to 350°F (175°C). Line a 9×5-inch loaf pan with parchment paper or grease it thoroughly.
In a large mixing bowl, mash the overripe bananas with a fork until smooth with just a few small chunks remaining.
Add the melted butter to the mashed bananas and mix well. Stir in the sugar, beaten egg, and vanilla extract until fully incorporated.
In a separate bowl, whisk together the flour, baking soda, salt, cinnamon, and nutmeg. Gradually fold the dry ingredients into the banana mixture, stirring just until combined.
Pour the batter into your prepared loaf pan and smooth the top. Bake for 55-60 minutes, or until a toothpick inserted into the center comes out clean.
Allow the banana bread to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
While the bread cools, beat the softened cream cheese and butter together until smooth and fluffy (about 2-3 minutes).
Add the sifted powdered sugar gradually, then incorporate vanilla and salt. Continue beating until the frosting is light and creamy—about 3 minutes total.
Once the banana bread has completely cooled, spread the cream cheese frosting generously over the top. For an elegant finish, create decorative swirls with the back of a spoon, or sprinkle with chopped walnuts or a light dusting of cinnamon.