Preheat your oven to 170C/150C fan. Grease and line a 9-inch springform (or equivalent – much smaller and it should have high sides) cake tin.
In a pan, gently melt your butter. Add your soft brown sugar, and stir until it forms a smooth-ish paste. Spread this evenly on the bottom of your cake tin.
Chop your two bananas for the top into discs and roughly chop your pecans. Arrange the bananas so they cover the bottom of the tin leaving as few gaps as possible. Scatter the pecans in the gaps.
In a large bowl, beat together the sugar, butter, bananas and eggs until roughly combined. Then, add your flour, baking powder and pecans and stir everything together very gently until just combined – it should still be lumpy, but no flour should be visible
Pour this mixture on top of your prepared bananas and pecans and place in the oven for anything from 40 minutes to an hour. It will depend on your oven. When it is cooked, a skewer will come out clean and it will be springy to press. If it is browning too fast, turn your oven down at least 20 degrees.
When baked, leave to cool for 10 minutes in the tin. Unclip the side of your tin, loosening the sides with a knife if you have to. Place a plate/cake-stand on top of your cake. Then, holding everything, flip your cake onto the cake stand so that the bottom is now the top. Remove the base and voila! A perfect upside-down cake – ready to eat or save for a good 2 days.
When making any cake that involves caramel, remember that no cake tin is 100% caramel-tight. So lay a baking tray below or some foil on the bottom of the oven to catch any drips before they become a nightmare to get off.