Whisk together first 5 ingredients until blended. Cover and chill.
Snap off tough ends of asparagus. Cook asparagus in boiling water to cover 2 to 3 minutes or until crisp-tender; drain. Plunge into ice water to stop the cooking process; drain.
Cook beans in boiling water to cover 3 to 5 minutes or until crisp-tender. Plunge into ice water to stop the cooking process; drain.
Cover and chill vegetables until ready to serve with dip. Garnish dip with fresh basil, if desired.
This is a great make-ahead appetizer for a summer party. The dip is actually better the next day. I used Greek yogurt instead of sour cream and a bit of extra lemon. Guest ate every last bite.
