Heat a deep pan or soup pot, and add the oil. I used sunflower oil for the flavour, but of course you could use any other oil without a strong aroma.
Add the chopped leeks and the thyme and saute for about 3-4 minutes, till the leeks are soft.
Add the fennel, mango and apple and stir.
Add the walnuts and stir. Season with salt and pepper.
Add the turmeric and stir well for 2-3 minutes, till the raw smell disappears.
Saute for 3-4 minutes till everything begins to soften.
Add the stock, stir. Bring the soup to a boil and then let it simmer on low for about 15 minutes, stirring periodically.
Turn off the stove and let the soup cool.
Puree or blend the soup to a smooth creamy liquid. Remember not to puree when the liquid is hot, and to puree it in very small batches. I have had many a bitter experience in pureeing soup only to have it spurt out of the blender all over me and the kitchen. And this soup has turmeric which has strong dyeing properties - so!
Pour the pureed liquid back into the soup pot, bring to a boil and then simmer. Check the seasoning, add more salt or pepper if required, and then again simmer for 5 minutes.
Serve hot with a garnish of toasted sliced walnuts, a few chopped fennel fronds and a drizzle of honey or maple syrup. I have garnished with purple basil flowers and the edible flowers add another dimension of flavour to the Soup.