Preheat the oven at 175ºC/350ºF conventional oven and prepare a 23 cm/9-inch springform with parchment paper.
Start by browning the butter over medium heat in a frying pan. Once browned, pour it into a bowl and let it cool down slightly in the refrigerator while preparing the other ingredients. It doesn't need to cool down completely.
90 g butter
Sift the all-purpose flour, baking soda, baking powder and salt together in a bowl. Mash the bananas and set it aside.
240 g all-purpose flour, 1 teaspoon baking powder, 1 teaspoon baking soda, ½ teaspoon salt
Add the brown butter and granulated sugar in a bowl and whisk it together with a hand whisk or in a stand mixer.
150 g granulated sugar
At low speed, add the eggs one at a time until they are incorporated into the batter.
2 eggs
Continue on a low speed, add ½ of the flour mixture and mix it in. Then add the mashed banana, whole milk and vanilla extract and mix it in.
240 g overripe bananas, 100 g whole milk, 1 teaspoon vanilla extract
Add the chocolate chips to the last ½ of the flour mixture and mix it together. Then add it to the batter and mix until just combined.
40 g mini chocolate chips
Use a rubber spatula, give the batter a final mix, making sure everything has been combined.
Add half the cake batter into the prepared springform. Then gently sprinkle half of the cinnamon crumble in an even layer. Add the remaining cake batter and even it out. Finally top it with the remaining crumble.
Bake it for 45-50 minutes or until the cake tester comes out clean. Once baked, let the cake cool. After 10 minutes, gently drag a thin knife along the edge of the cake to release the cake from the springform. Let it cool down completely on a wire rack.