The best way to add leafy greens to a soup is to shred them into the bottom of the bowl and pour the hot soup over. The heat softens them, but they keep their freshness and flavour.
Home grown leafy greens have so much flavour, even softened in the soup the Kale, English Spinach and fenugreek sprouts kept all the flavour and freshness.
The soup was a Leek and Potato, not vichyssoise more of a peasant dish with a ham hock and chicken stock, with black eyed peas. The way to get the leek flavour right through the soup is to saute the leeks in plenty of olive oil, then add the chopped potatoes and cook them with the leeks till the flavour is right through the potatoes.
Potatoes are amazing for soaking up flavour, if something has to much chilli in cook some potatoes through it to take up the heat.