Preheat and prep.
Heat oven to 175°C (350°F). Grease and line a loaf pan. Do this first. Future-you will be grateful.
Mash bananas.
Mash in a large bowl until mostly smooth. Lumps are fine. This isn’t a science project.
Mix wet ingredients.
Add butter, sugar, eggs, and vanilla. Whisk until glossy and smooth.
Mix dry ingredients.
In another bowl, combine flour, baking soda, salt, and cinnamon. Stir well.
Combine gently.
Fold dry into wet until just mixed. Stop early. Overmixing ruins texture.
Make streusel.
Mix brown sugar, flour, and cinnamon. Cut in cold butter with fingers until crumbly.
Assemble.
Pour batter into pan. Level it. Sprinkle streusel generously. Be dramatic.
Bake.
Bake 50–55 minutes. Toothpick should come out with moist crumbs.
Cool slightly.
Let cool 15–20 minutes. Don’t rush or it’ll crumble.
Slice and serve.
Cut thick slices. Pair with coffee. Smile.