Trim off the woody ends of the asparagus, peel and cut into 2cm slices.
Boil the water with a little salt and sugar and simmer the asparagus 20-25 minutes, until quite soft.
Drain the asparagus, keeping the cooking liquid. Blend the asparagus in half of the cooking liquid.
In a large saucepan, melt butter and add flour to form a roux, stirring. Slowly pour in the hot milk, stirring constantly, to make a smooth paste. Add pureed asparagus and as much of the remaining cooking liquid to reach a consistency you like.
Stir in the cream and heat but do not boil. Season with salt and pepper and serve sprinkled with chives.