Begin by peeling the celery root and cutting it into chunks. Dice the onion and mince the garlic to set the foundation for a flavorful soup.

In a pot, heat a couple of tablespoons of olive oil over medium heat. Add the diced onion and minced garlic, sautéing until fragrant, about 5 minutes.

Stir in the celery root chunks and pour in the vegetable broth. Bring the mixture to a boil, then reduce the heat and let it simmer for 20-25 minutes, until the celery root is tender.

Carefully transfer the soup mixture to a blender or use an immersion blender in the pot. Blend until smooth, adding more broth if you prefer a thinner consistency.

Return the blended soup to the pot and stir in the spirulina powder along with the soy milk or cream. Heat gently for an additional 5 minutes, allowing the flavors to meld.

Ladle the warm soup into bowls. For a finishing touch, drizzle with olive oil or sprinkle with fresh herbs for an inviting presentation.