Preheat your oven to 400 degrees Fahrenheit (200 degrees Celsius). Toss the trimmed asparagus with 1 tablespoon of olive oil, salt, and pepper on a baking sheet. Roast for 10 to 12 minutes until tender-crisp. Set aside about 1/4 cup of the roasted asparagus tips for garnish.
While the asparagus roasts, heat the remaining 1 tablespoon of olive oil in a large pot or Dutch oven over medium heat. Add the chopped onion and cook until softened, about 5 minutes.
Add the minced garlic and cook for 1 minute more until fragrant.
Add the vegetable broth and bring the mixture to a simmer.
If using cashews, soak them in hot water for 10 minutes, then drain. Add the roasted asparagus (reserving the tips) and the soaked cashews to the pot. Simmer for 5 minutes.
Carefully transfer the soup mixture to a blender. Blend until completely smooth and creamy. If you do not have a high-speed blender, blend in batches.
Return the soup to the pot. Stir in the fresh lemon juice. Heat gently if needed, but do not boil. Adjust salt and pepper to taste.
Ladle the soup into bowls. Garnish each serving with the reserved roasted asparagus tips and fresh parsley.
Notes
For a dairy-free version, use vegetable broth and the cashews for creaminess as directed. Avoid adding any cream or milk.
For a richer, non-vegan version, substitute 1/2 cup of heavy cream for the cashews and omit the soaking step. Add the cream at the end with the lemon juice.
If you prefer a quicker method, you can steam or boil the asparagus instead of roasting, though roasting adds depth of flavor.