Wash the asparagus thoroughly, cut off the woody lower ends. Peel the asparagus. Boil 1.25 litres of water with salt and 1 pinch of sugar. Add the asparagus peel and simmer covered for about 20 minutes.
In the meantime cut the asparagus into pieces. Drain the asparagus skins, let them drain well and collect the asparagus water. Pour asparagus water back into the pot, bring to the boil and add asparagus pieces. Cook for about 15 minutes. Drain the asparagus, collect the asparagus water and measure 1 litre of liquid.
Heat butter in a pot, dust with flour, sweat it and gradually deglaze with asparagus water and cream, stirring constantly. Bring to the boil, simmer for 5 minutes, season to taste with salt, pepper, sugar and lemon juice. Add asparagus, heat up again briefly. Serve garnished with chervil