Begin by heating the oil in a large pan. Add the onions and celery to the pan. Cook over medium heat for about 10-12 minutes or until soft.
Add the celeriac and apples to the pan. Cook for 3-4 minutes.
Add the stock along with two sprigs of fresh thyme. Cover and simmer on low for 35-35 minutes or until the celeriac is tender.
Remove from the heat. Remove thyme stems; then blend until smooth with an immersion blender. Stir in crème fraîche.
To serve, spoon the soup into bowls. Drizzle with crème fraîche and olive oil. Place the lid onto the bowl and top with garnishes, including chopped hazelnuts, sliced red pepper, diced apples, edible flowers, thyme leaves, and fried sage leaves*.
*Fried Sage Leaves: Heat 2-3 tablespoons of olive oil in a pan. Add the sages leaves, 5 or 6 at a time. Fry for 8-10 seconds. Remove from the oil with a fork. Transfer to a paper towel-lined plate.*You can find the bowls I used in this recipe here.