Preheat your oven to about 180°C
Put your sour cream in a bowl and stir smooth
Using a fork, mush your banana smooth as well.
Mix the banana with the sour cream
Using an electric whisk, beat the eggs and the sugar until it's white and fluffy
Mix the flour, baking powder and vanilla sugar in a separate bowl before adding it to the egg mixture.
Mix the banana mixture with the batter
Measure your 50 grams of butter and place it in a microwave friendly bowl, and then place a sheet of paper over it.
Melt the butter in the microwave before mixing it with the rest of the batter. It is really the simplest way of melting butter and uses a lot less energy than a stove.
Prepare the cake pan so that the cake won't stick. I use butter and bread crumbs. If you have a non-stick cake pan, you're fine :)
Pour the batter into the cake pan, place on a rack in the middle of the oven.
Bake for about 30-40 minutes. It should be golden and baked all the way through.
Enjoy! Preferably on a sunny autumn day. It's really good with some whipped cream to it, but I like mixing Greek yoghurt with a bit of vanilla and some honey for a fresher option. Try it! :)