cut 1 ½ inches off the tops of half the asparagus and set aside for a garnish. Slice the remaining asparagus.
Melt 2 tablespoons of the butter in a large saucepan, being careful not to let it burn. Sauté the sliced shallots for 2-3 minutes, until soft.
Add the asparagus and sauté over low heat for 1 minute.
Stir in flour and cook for 1 minute. Stir in the stock or water and lemon juice and season with salt and pepper. Bring to a boil, half cover the pan, then simmer for 15 – 20 minutes, until the asparagus is very tender.
Cool slightly and then process in the soup in a food processor or blender until smooth. Press the pureed asparagus through a sieve into a clean saucepan. Add the milk by pouring and then stirring it through the sieve with the asparagus so as tot extract the maximum amount of asparagus for the soup puree.
Melt the remaining butter and sauté the reserved asparagus tips gently for 3-4 minutes, to soften.
Heat the soup gently for 3-4 minutes. Stir in the cream and asparagus tips. Continue to heat gently, then serve sprinkled with chopped fresh chervil.