Preheat the oven to 200°C.
Wash the sweet potatoes, cut off the ends and cut into quaters. Roast in the oven for 45 minutes.
Cut the shallot in quaters.
In a big pot, whisk together vegetable broth, coconut milk, salt, pepper and nutmeg. Add sweet potatoes, shallot and rosmary. On a medium heat, bring to a boil and let then simmer for 10 minutes.
After that, purre with a mixer to an even soup.
Serve with crushed walnuts.