Preheat the oven to 170ºC and line a 22cm cake tin with baking paper, greasing the sides (if you are using a loose-bottomed pan, place a folded sheet of foil around the base in case some of the maple syrup leaks).
Pour maple syrup into the base of the cake tin. Slice 3 bananas in half lengthways and layer them, cut-side down.
For the cake, rinse the remaining 3 bananas under cold water, cut off ends then blend banana and skins together in a food processor.
Beat butter and sugar until thick and pale. Add eggs, 1 at a time, beating well after each addition. Beat in vanilla, then fold in the flour, baking soda and cinnamon.
Fold in bananas and pour the batter over bananas in tin.
Bake for 1 hour 15 minutes until a skewer inserted into the centre comes out clean.
Meanwhile for the toffee sauce, combine butter, sugar, and cream in a medium saucepan and bring to a boil over medium-high heat. Reduce heat to medium (so sauce doesn't boil over) and boil, stirring frequently, until sauce thickens and darkens slightly, about 4 minutes.
Once cake is cooked. Allow to cool in the tin for 10 mins before turning out onto a plate.
Pierce hot cake all over with a skewer, then drizzle over half the sauce.
Best served warm with remaining sauce and ice-cream but it’s also delicious at room temperature.