Finely dice the spring onions, peppers, ginger and garlic. Dice the potatoes, cut the leek into slices.
Melt the butter in the pan. Sauté the spring onions and spices in it for 2 minutes and remove. Briefly sauté the potatoes and leeks, dust with turmeric and fill up with broth. Cover and cook over medium heat for 20 minutes.
Puree the soup, add coconut milk, bring to the boil again.
Pluck and chop the coriander leaves. Add the spring onion and spice mixture to the soup, add salt if necessary. Serve immediately.