Snap off tough ends of asparagus. Remove scales from stalks with a knife or vegetable peeler, if desired. Cut asparagus spears in half crosswise. Bring 1/4 cup chicken broth to a boil in a medium saucepan. Add asparagus; cover and cook over medium heat 5 minutes or until crisp-tender. Set aside asparagus in broth.
Coat a small saucepan with cooking spray, and place over medium-high heat until hot. Add onion; saute until tender. Add remaining 3/4 cup broth and potato. Bring to a boil; cover, reduce heat, and simmer 15 minutes or until potato is tender.
Combine potato mixture and asparagus, including broth, in container of an electric blender or food processor; cover and process until smooth. Transfer mixture to a bowl; stir in milk, salt, and pepper. Cover and chill. Stir before serving. Garnish with lemon rind strips, if desired.