Sauté the onion in the olive oil in a heavy-based pan. Add the celeriac and saffron, stirring occasionally. Add the white wine and stock. Allow the mixture to simmer for 25 minutes, until the celeriac is cooked. Purée the soup until smooth using a hand blender.
Fold in the crème fraîche and season the soup with salt and pepper. Reduce until it slightly thickens. Pour into attractive bow