Upside Down Walnut Banana Bread

Heat the oven to 170°C with a rack in the middle — if using a springform tin, place a sheet pan on the rack below to catch any drips.

For the topping, grease a 23×23cm (9×9") square metal pan with butter and line it with a strip of parchment running up both sides and across the base.

Roughly chop the walnuts and scatter them over the base of the pan.

Heat the brown sugar, maple syrup, butter, milk, vanilla and salt together in a small pot over medium-low heat until melted, then stir and cook until combined and just bubbling.

Pour the mixture over the walnuts, then chill the pan (on a tea towel, to protect the fridge shelf) until firm.

For the banana bread, cook the butter, brown sugar, cinnamon and mashed bananas together in a medium saucepan over medium-low heat, stirring regularly, until the bananas soften and the sugar dissolves. Remove from the heat and let cool slightly.

Whisk the eggs, salt, vanilla, sour cream and oil together in a mixing bowl.

Pour in the cooled caramelised banana mixture and whisk again.

Add the flour and baking powder and mix until just combined.

Pour the batter over the chilled walnut topping in the pan.

Bake on the middle rack for 20 minutes, then rotate the pan 180 degrees and bake for another 15 to 20 minutes, until the edges are golden and a toothpick comes out clean.

Remove from the oven and let cool for exactly 10 minutes — not longer, or the caramel sets and sticks to the pan instead of releasing.

Place a serving plate or board upside down over the pan, then, holding both firmly, flip it over so the cake drops out onto the board.

Leave to cool for at least 10 minutes, or a few hours, before cutting into 9 squares and serving.