Step 1

In a Dutch oven, heat butter over medium-high heat. Add asparagus and onion; cook and stir 10-12 minutes or until asparagus is crisp-tender.

Step 2

Add broth; bring to a boil. Reduce heat; simmer, covered, 6-8 minutes or until asparagus is tender. Remove soup from heat; cool slightly. Stir in lemon juice, tarragon, salt and pepper.

Step 3

Process in batches in a blender until smooth. Serve with yogurt and lemon zest.