Pre-heat the oven to 400 degrees. Line a baking sheet with parchment paper and set aside.

Heat 2 tablespoons of olive oil in a large Dutch oven (or a heavy bottom pot) in medium heat. Add in the chopped onion and sauté until translucent, 4-5 minutes.

Stir in the cauliflower florets, celery root, water, 2 teaspoons salt and 1/2 teaspoon freshly ground black pepper. Cover the pot, lower the heat to medium-low and cook until vegetables are soft, 15-20 minutes.

Meanwhile, cut the stems of the mushrooms and discard. Slice them into 1/2-inch slices. Spread them on the baking sheet. Drizzle with 1-tablespoon olive oil. Sprinkle with 1/2 teaspoon salt and 1/4 teaspoon of black pepper. Bake in the oven for 10-15 minutes. Give them a gentle stir hallway through. Set aside.

When the vegetables are cooked add in the roasted garlic, puree soup with an emersion blender (or a food processor or an upright blender) until completely smooth and creamy. Taste for seasoning and add if necessary.

Pour the now-pureed soup back into the pot, stir in the tamari, and heat for 5-10 minutes, stirring occasionally.

When ready to serve, ladle the soup into bowls. Top it off with roasted shiitake mushrooms and garnish it with chopped chives.