Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line it with parchment paper for easy removal.
In a large mixing bowl, combine the mashed bananas, granulated sugar, brown sugar, melted butter, beaten egg, and vanilla extract. Mix until well combined.
Stir in the baking soda and salt until evenly distributed.
Gradually add the flour to the banana mixture, stirring gently until just combined. Be careful not to overmix.
Fold in the Biscoff spread until swirled throughout the batter. If using, add the chopped walnuts or pecans and mix gently.
Pour the batter into the prepared loaf pan and smooth the top. Drizzle a little extra Biscoff spread over the top if desired.
Bake in the preheated oven for 55-65 minutes, or until a toothpick inserted into the center comes out clean.
Allow the bread to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.