Preheat the oven to 180 degrees Celcius or 355 degrees Farenheit.
Melt the butter in a saucepan or microwave. When using the microwave go for short bursts of 30 seconds at 750W, stirring in between as it melts. When the butter has fully melted, mix the sugar and butter in a large mixing bowl. Use a mixer at a medium setting for about 3 minutes.
Add the eggs one by one, fully stirring in the previous one with the mixer before adding the next. When all the eggs have been added, stir at a medium-high setting for 2 minutes, followed by a low setting for another 5 minutes. This ensures the egg-whites become very fluffy and will give the cake a very nice texture.
Add the milk (and potential syrups if using those) and stir it in on low setting for a minute before adding the dry ingredients (flower, baking powder, salt). Use a spatula to stir in the dry ingredients. When its stirred in you can use the mixer on a low setting for 2 minutes to ensure the batter is smooth, without any clumps of flour.
On a plate, mash the bananas into a puree. Are your banana's a bit on the green side, or just not soft enough to be properly pureed? Pop them in the microwave for a minute at 750W and they'll be easier to mash! (When doing this, make sure to let the banana's cool down before adding them into the batter!) Stir the banana puree into the batter with a spatula.
Now is the time to also stir in any extra's you might want to add. A favourite of mine is combining cinnamon, raisins and walnuts. Or vanilla syrup (added in step 4) and chocolate chips.
When it's all stirred together properly, you carefully scoop the batter into a cakepan. You can use multiple smaller size cakepans or one larger one. Make sure not to tap or shake the batter too much as this will negate the fluffyness we tried to stir in in step 3.
Put the cake in the middle of the oven and bake for an hour. Check with a wooden toothpick (or something wooden like it) if the cake is done: if the pick comes out clean the cake is done, if there's batter sticking to it, it needs to go longer. If it needs to go longer, prolongue the time with 10 minutes and check again and so on and so forth until the pick comes out clean.
The cake will need to cool down, to make sure it doesn't fall apart while you're cutting into it. You can carefully take it out of the cakepan and leave it on a cooling rack, or leave it in the cakepan to cool off.
Serve it at a party, cut it in slices and store it in the freezer or have it as desert! Enjoy :)