Heat oil in a large stock pot over medium high heat. After oil is hot, add onion and garlic, stir and cook for 2-3 minutes, until garlic is golden and onion is soft and translucent.
Add the asparagus to the pot and cook for 2 minutes. Add the broth and celery root. Bring soup to a boil, then turn heat down to low and simmer for 15 to 20 minutes or until asparagus and celery root are fork tender.
Transfer soup into a blender, add the tahini, lemon juice, cumin, coriander, and salt and pepper.
Blend until smooth and creamy. Taste and adjust seasoning as needed.
Return the soup back to the stock pot and bring to a simmer over medium heat. Serve and garnish with sesame seeds.