Melt the butter in a saucepan. Add 120 ml of water, bring to the boil and pour in the rice. Let it cook for about 5 minutes. Pour in the milk and cook for another 20 minutes. Add the salt and vanilla sugar. Mash the bananas (amount to taste) with a fork and stir into the rice.
Puree the strawberries in a blender and serve as a sauce.
The rice doesn`t need sugar as the bananas are sweet enough. Fully / overripe bananas are also suitable for use as leftovers. Maybe add some sugar to the sauce if the berries are too sour, but I`ve never needed sugar there.
Incidentally, for lack of short grain rice, I already made the whole thing with long grain rice and it tasted just as good.