Finely puree the banana. Peel the ginger and grate finely. Mix thoroughly with vinegar, salt and mustard flour. Add approx. 5 - 6 tablespoons of water as required.
The mustard should be relatively thin because the mustard flour will still swell. Leave the mustard open for approx. 24 hours. Then fill into glasses and store in a dark place.
Let it mature for at least 2 weeks until it has developed its full flavor.