In a large soup pot, add asparagus, onion and 1 cup chicken broth. Cover and bring to a boil over high heat. Reduce heat and simmer partially covered until asparagus and onions are tender (about 15 minutes).

Place half of asparagus mixture in a blender. Remove center piece of blender lid (to allow steam to escape); secure blender lid on blender. Place a clean towel or piece of paper towel over the opening in the blender lid (to avoid splatters). Blend until smooth. If needed, add a little chicken broth so it puree’s easily. Pour pureed soup into a bowl. Repeat procedure with remaining asparagus and add to same bowl.

In the same soup pot, wipe out any remaining onion chunks, if any. Melt butter; using a wire whisk, stir in flour, salt and pepper. Cook, stirring constantly with whisk until mixture is blended smooth (about 1-2 minutes). Whisk in the remaining chicken broth. Stir about 5 minutes until blended well and slightly creamy.

Stir in asparagus puree and milk.

Put sour cream into a medium bowl and add 2 ladlefuls of hot soup. Blend well with a wire whisk and add to soup pot along with lemon juice. Stir and enjoy.