Kumara and Orange Soup

500g kumara (sweet potatoes)
100mls dry white wine
1500mls chicken stock
100mls orange juice concentrate
50g walnuts, finely ground
2 tablespoons butter
2 tablespoons flour
500mls milk
salt and pepper

Scrub or peel the kumara and cut into chunks. Place in a saucepan with the wine and about 500mls of the chicken stock and simmer until soft. Blend in a food processor with the grated walnuts until smooth. Stir in the orange juice and the remaining stock. Melt the butter, stir in the flour. Cook a further minute then whisk in the milk and simmer until the mixture thickens and makes a thin white sauce. Add to the kumera mixture and whisk to blend thoroughly. Reheat, adjusting the seasoning as necessary. Serve garnished with a little light sour cream and some grated walnuts.