Heat a splash of oil in a saucepan and fry the onion, garlic, carrots and celeriac for 4-5 minutes, or until the onion is translucent.
Add the curry powder and turmeric and cook for about a minute, then pour in the stock and the cream. Season with a little salt and freshly ground pepper.
Let the soup simmer gently until the carrots and celeriac are completely tender. About 15-20 minutes - depending on the size of the pieces.
Meanwhile, peel and clean the prawns, drizzle with lemon juice and season with salt and freshly ground pepper.
Blend the soup until smooth, season to taste with salt and freshly ground pepper, and divide between 4 bowls.
Top with crème fraîche, prawns and a sprinkling of herbs. Serve immediately.