Preheat the oven to 180 C (350 F). Take out a loaf pan, grease it with a bit of butter, and line it with a piece of baking paper. Set aside.
Sieve together the flour, baking soda, salt, and cinnamon. By doing that you'll ensure that there are no lumps in the batter, and, at the same time, you'll mix well all the dry ingredients. Set aside.
Using a handheld or standing mixer fitted with a paddle attachment beat the butter and sugar together until smooth and creamy. Mix on high speed for 2-3 minutes.
Add the eggs, one at a time, and beat well on medium speed. The texture will become weird and lumpy but don't worry, once you add the flour it'll come back to normal.
Using a fork, mash the bananas and add them to the batter together with the vanilla extract. Mix well.
With the mixer on a low speed, slowly add the flour mixture to the batter using a spoon. Mix after each addition, until there's no flour visible.
Pour the batter into the prepared loaf pan and bake for 45-50 min until the toothpick inserted in the middle of the banana bread comes out with only few crumbs on it.
