Preheat oven to 180°C (350°F). Grease and line a loaf tin.
In a large bowl, whisk together melted butter, condensed milk, sugar, and eggs until smooth.
Stir in the mashed bananas and vanilla essence.
In another bowl, sift together flour, baking powder, bicarbonate of soda, salt, and cinnamon.
Gently fold the dry ingredients into the wet mixture until just combined. Do not overmix.
Pour the batter into the loaf tin and smooth the top.
Bake for 50–60 minutes, or until a skewer inserted into the centre comes out clean.
Allow to cool slightly before slicing.