Preheat the Oven: Set the oven to 350°F (175°C) and grease a loaf pan or line it with parchment paper.
Mix Dry Ingredients: In a large bowl, sift together the all-purpose flour, baking powder, baking soda, and salt.
Combine Wet Ingredients: In a separate bowl, mash the ripe bananas. Add the sugar, melted butter, eggs, and vanilla extract, mixing until smooth.
Make the Batter: Gradually fold the dry ingredients into the wet ingredients until just combined. Pour the batter into the prepared loaf pan.
Prepare the Crumble Topping: In another bowl, combine brown sugar, flour, and cinnamon. Add the cold butter and mix until the texture resembles coarse crumbs.
Add Crumble and Bake: Sprinkle the crumble topping evenly over the batter in the loaf pan. Bake for 50–60 minutes, or until a toothpick inserted in the center comes out clean.
Cool and Serve: Let the banana bread cool in the pan for 10–15 minutes, then transfer it to a wire rack to cool completely before slicing and serving.