Spiced creamed parsnip soup with sherry

Ingredients
115 g/4 oz/ 1/2 cup butter
2 small or 1 large onion, sliced
1 kg/2 1/4 lb. parsnip peeled and chopped into 1 in cubes
10 ml/2 tsp curry powder
30 ml/2 tbsp medium sherry
1.2 litres/2 pints/ 5 cups chicken or vegetable stock
salt and pepper to taste
plain yogurt, to serve

Melt the butter in a pan, add the onion and sweat gently without allowing to burn. Add the chopped parsnip, coat with the butter and stir in the curry. Add sherry and cover with a lid. Cook over a low heat for 10 minutes or until the parsnips are softened, making sure they do not color.
Add the stock  and season to taste. Bring to a boil then simmer for about 15 minutes  or until the parsnips are soft. Remove from the heat, pure with a stick/immersion blender. Serve with a swirl of yogurt.