Meanwhile, rinse watercress and roughly cut off the upper large leaves from stems.
When the onions are translucent, add turmeric, watercress stems and 750 ml water (ideally hot, the cooking time will be faster). Salt and pepper. Let it simmer for about 15 minutes.
Only then, thus at the very last moment, add watercress leaves, stir and immediately mix with a blender.
Adjust the seasoning (and amount of water) if necessary.