Bring all the ingredients to room temperature. Grease a 23 cm springform cake pan with butter and line the base with parchment paper. Cut strips of parchment paper, approximately 5–6 cm wide, to line the sides of the pan as well.

Generously butter the base of the pan with the 60 g of butter, then sprinkle evenly with the 120 g of sugar.

Peel 4 bananas and cut each lengthwise into 2 or 3 strips. Arrange them over the base of the pan, cut side down, covering the entire surface so that no sugar is visible and there are no gaps between the pieces.

Mash the other 2 bananas and drizzle with a little lemon juice to help prevent discoloration.

In a mixing bowl, beat the 150 g of softened butter with the brown sugar using a hand mixer until the mixture is creamy and smooth.

With the mixer running, add the eggs one at a time, beating well after each addition. Mix in the mashed bananas, sunflower oil, salt, and baking soda.

Add half the flour and mix until combined. Add the buttermilk or whole milk, followed by the remaining flour. Gently fold everything together with a spatula until just incorporated.

Fold in the chocolate chips with the spatula, distributing them evenly throughout the batter.

Carefully pour the batter over the banana slices, spreading it evenly without disturbing the arrangement.

Preheat the oven to 160°C (320°F) using the fan setting. Bake on the middle rack for approximately 1 hour, or until a knife inserted into the centre comes out clean, without any uncooked batter.

Leave the cake to rest in the pan for 5–10 minutes. While it is still warm and the caramel remains runny, carefully invert it onto a serving plate. Remove the pan and parchment paper.