This herby soup, also known regionally as Frankfurt grüne soße (green sauce), is prepared with nine fresh wild herbs – hence the name loosely meaning 'the green nines'. While the dish is traditionally eaten on Holy Thursday before Easter, the origins are likely to outdate Christianity and can be traced back to the Celts and Germanic tribes. You're completely free to experiment with your choice of herbs including stinging nettle, wild garlic, ground elder, ribwort, sorrel, ground-ivy, borage, garlic rue and even daisies.