In a large bowl, add the browned butter mixture with instant coffee, oil, and light brown sugar. Whisk until well combined. Add the eggs, vanilla paste, mashed bananas, and Greek yogurt. Mix until smooth and fully incorporated.

Sprinkle in the baking powder, baking soda, and salt and mix. Combine the flour with cinnamon powder, then fold into the batter. Mix just until combined — do not overmix.

In a saucepan, melt the butter and light brown sugar over low-medium heat, stirring until well combined and slightly bubbly. It doesn't need to be fully smooth like a traditional caramel — just combined and glossy.

Preheat the fan oven to 170°C (338°F) and line an 8x8-inch square baking tray.

Pour the prepared caramel into the pan and spread evenly. Cut the bananas into thick half-moon slices and arrange over the caramel. Add walnuts.

Pour the cake batter over the bananas and spread it evenly.

Bake for 50-60 minutes. Start checking for doneness at the 45-minute mark by inserting a skewer into the center, it should come out clean or with a few moist crumbs.

Let the cake cool in the pan for 10 minutes, then carefully flip it onto a serving plate while still warm but not hot.