Preheat the oven to 350°F(177C°). Grease 8 1/2 * 4 1/2 inch (21,5*10,5cm) loaf pan and line the bottom and sides with parchment paper, about 2 inches(5 cm) of overhang on each side. If you like, you can grease and flour the dish instead of parchment paper.
Mix the flour, cinnamon, baking soda and salt(if you are using) in a medium bowl, set aside.
Place the bananas in a large bowl and mash with a fork. If you slice the bananas, you can easily mash the bananas.
Add the melted butter, milk, sugar and mix with a whisk or a spoon/spatula. Mix in the egg and add the vanilla and mix. Finally add the flour and mix until incorporated.
Place the mixture into the pan and bake for 40-45 minutes or until a toothpick comes out clean that is inserted in the center. Let it cool in the pan for 10 minutes and then let it cool completely on a wire rack. Slice when it completely cools.
Well wrapped banana bread stays fresh up to 2-3 days at room temperature and up to a week in the fridge.