Sorrel goes in for the last two minutes and no longer — it turns from green to olive almost as you watch, and the sourness goes flat with it. The window for this soup is about eight weeks and there is no substitute worth making.
It did not make it into the plan for these seven days.
The method above is what decides the dish, not a step-by-step recipe. The link runs a web search on the name: this page has no vetted sources of its own, and will not invent any.