In a large pot, add onion, leeks, celery and garlic with a small splash of water. Cook over medium heat for about 5–7 minutes until softened.
Add the vegetable broth and bring to a gentle simmer.
Add the chopped asparagus and cook for 5–7 minutes, just until tender and bright green.
Transfer most of the soup to a high-speed blender. Add the spinach, fresh dill and optional cashew cream. Blend until silky smooth.
Return the blended soup to the pot with the remaining soup. Stir in the lemon juice and black pepper.
Warm gently before serving.