Mix lemon juice and milk together and set aside.

Mix flour, baking soda, vanilla and salt together in a bowl.

Mix sugar and eggs at high speed until fluffy. Add dark brown sugar and softened diced butter. Mix at high speed until you get a thick but airy batter.

Add half of the flour mix and half of the milk mix to the eggs and stir together with a spoon. Do not overmix. Add the rest of the flour mix and milk mix and stir slowly until you get a runny batter.

Mash the bananas with a fork and add them to the batter. Stir slowly to mix.

Spray a round cake pan (22 cm) with non-stick spray or butter it. Pour the batter into the cake pan.

Bake the banana cake at 180 degrees C (without fan) for 45-50 mins. Cover the cake with foil after 25-30 minutes if the cake is getting too dark.

Check when the cake is done. Insert a toothpick into the center of the banana cake to see if the crumb has set. If it comes out clean, the cake is done. If it comes out with crumbs clinging to it, the banana cake needs more time in the oven.

Let the banana cake cool off for 15 minutes on a baking rack. Then put the banana cake in the fridge until it's room temperature.

Spread the frosting in a thick layer all over the cake once the cake has completely cooled.

Sprinkle with dark chocolate if desired.