This adaptation of the classic Greek egg-and-lemon soup can be made a day ahead of time and served warm or cold. For this menu, I prefer to serve it warm.
Wash asparagus. Break off woody ends of asparagus and reserve, then cut tips off asparagus spears and reserve. Cut asparagus stalks into 1-inch pieces. (If you use thick asparagus, peel the bottom 3 inches of the stalk with a vegetable peeler first, then reserve the peels along with the woody ends.) In a saucepan over high heat, place asparagus ends (and peels) and chicken broth. Cover, bring to a boil, and then immediately remove mixture from heat and let rest 15 minutes. Strain broth and reserve. Discard asparagus ends (and peels).
Place 4 cups of water and ½ teaspoon salt in a small saucepan. Bring to a boil, then blanch the asparagus tips 2 minutes, or until bright green and barely cooked through. Remove tips from hot water and plunge into a bowl of ice water until chilled. Drain and reserve to use as garnish for the soup.
In a large soup pot over medium heat, melt butter and add chopped celery, onions, and leeks. Saute until softened, about 6 minutes. Season with salt and pepper to taste. Add asparagus stalk pieces; stir. Add infused chicken broth and 2 cups water. Increase heat to high and bring to a boil, then reduce heat to medium-low and simmer, covered, about 5 minutes, until asparagus is tender. In a blender, puree soup in batches. Return pureed soup to the pot and allow to cool about 5 minutes, or until lukewarm.
In a small bowl that can withstand heat, whisk together eggs and ¼ cup lemon juice until creamy and well mixed. Slowly add 1 cup of the slightly cooled soup, whisking constantly. Pour egg-soup mixture back into the soup pot, whisking constantly. Cook soup over low heat, whisking constantly, until soup is thickened slightly and the temperature reaches 160 degree on an instant-read thermometer. Do not allow soup to boil. Whisk in snipped dill and additional 2 tablespoons lemon juice. Add salt and pepper to taste.
Refrigerate soup in a covered container up to 24 hours. Reheat gently on low heat before serving. Place asparagus tips and a sprig of dill in the center of each bowl of soup as a garnish.