500g fresh asparagus, trimmed and cut into 2.5cm pieces
80g chopped onion
400ml chicken stock
2 tablespoons plain flour
1 teaspoon salt
1 pinch ground black pepper
125ml soured cream
1 teaspoon fresh lemon juice
In a large saucepan, combine asparagus, chopped onion and 125ml of the chicken stock. Cover, and bring to the boil over high heat. Reduce heat, and simmer uncovered until asparagus is tender, about 12 minutes. Process the mixture in a blender to puree the vegetables. Set aside.
In the same saucepan, melt the butter over medium-low heat. Stir in the flour, salt and pepper. Cook, stirring constantly for 2 minutes. Whisk in the remaining chicken stock, and increase the heat to medium. Cook, stirring constantly until the mixture boils. Stir in the asparagus puree and the milk.
Put the soured cream in a small bowl, and stir in a ladleful of the hot soup. Add the soured cream mixture and the lemon juice to the soup. Stir while heating the soup to serving temperature, but don't allow it to boil. Serve immediately.