Grease and line a 2 lb loaf pan with parchment paper.
Whisk the flour and baking powder together in a large mixing bowl.
Add the softened butter, mashed bananas, light brown sugar, golden syrup, beaten eggs, and vanilla bean paste.
Beat together just until evenly combined. The batter should be thick and spoonable rather than runny, but a few very small lumps of softened butter are fine.
Spoon the batter into the prepared loaf pan and level the top.
Bake at 360°F for about 33 minutes, then reduce the oven temperature to 350°F and continue baking for approximately 15 minutes, or until the center is set.
If the top is browning too quickly, loosely cover it with foil.
The loaf should be golden brown and set through the center. A skewer inserted into the middle should come out without wet batter.
Let the loaf cool in the pan for about 10–12 minutes, then transfer it to a wire rack.
For the best texture, allow the loaf to cool for 1½–2 hours before slicing.
Notes
Texture: This banana bread has a dense, moist, slightly squidgy texture rather than a light, cake-like crumb.Golden Syrup: British golden syrup gives this banana bread its distinctive caramel flavor and squidgy texture. If you can’t find golden syrup in the U.S., you can substitute an equal weight of light corn syrup, although the flavor will be milder.High Altitude: This recipe was developed and tested at approximately 8,600 feet and uses only 1 tsp baking powder to control the rise at high altitude. At substantially lower elevations, you may find that a little more baking powder is needed. See my Kitchen Guides for more help with high-altitude baking.