Trim tips and woody ends from asparagus spears and reserve, separately. Cut remaining spears into 1-inch lengths.
Blache tips in boiling water with 1/2 teaspoon salt for 2 minutes until bright green and tender.
Put woody ends in chicken broth in medium saucepan. Cover and bring to a boil. Remove from heat and leave covered for 15 minutes to steep. Strain ends from broth and throw away.
Cook onion, celery and leek in butter for 5 minutes until softened. Add 1-inch asparagus pieces and stir. Add strained broth plus 2 cups water. Bring to a boil, reduce heat and simmer, covered, about 5 minutes, or until asparagus is tender. Puree soup in pan with immersion blender, or in batches in a regular blender.
Whisk eggs with all but 2 tablespoons of lemon juice until creamy and frothy. When soup has cooled to lukewarm (about 5-10 minutes) stream one cup of soup into egg/lemon mixture, whisking constantly. Whisk soup-egg mixture back into soup pot. Place over medium heat and cook until slightly thickened, without boiling, or until temperature reaches 160 degrees.
Add remaining 2 tablespoons lemon juice and snipped dill. Add salt and pepper to taste. Garnish with blanched tips and a sprig of dill. Serve hot, room temperature, or cold.