Cut 1.5 inches off the tops of half the aspargus and set aside for garnish. Slice the remaining asparagus.
Melt 2 tbsp of butter in a large saucepan and saute the sliced shallots for 2-3 minutes until soft.
Add the asparagus and saute over low heat for 1 minute.
Stir in the 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 the sup in a food processor or blender until smooth. Press the pureed aspargus through a sieve into a clean sauce pan. Add the milk by pouring and stirring it through the sieve with asparagus as to extrace the maximum amount of asparagus puree.
Melt the remining butter and saute the reserved asparagus tips gently for 3-4 minutes to soften.
Heat the soup gently for 3-4 minutes. Stir in the cream and the asparagus tips. Continue to heat gently then serve sprinkled with chopped fresh chervil.