Creamy Celeriac and Apple Soup with Toasted Hazelnuts

Preheat oven to 350°F (175°C). Spread the hazelnuts on a baking sheet and toast for 8-10 minutes, or until fragrant and lightly golden. Let cool slightly, then roughly chop.

Heat olive oil in a large pot or Dutch oven over medium heat. Add onion and cook until softened, about 5 minutes. Add garlic and cook for another minute until fragrant.

Add celeriac and apple to the pot and cook for 5 minutes, stirring occasionally.

Pour in vegetable broth and add the thyme sprig (if using). Bring to a simmer, then reduce heat, cover, and cook for 20-25 minutes, or until the celeriac is tender.

Remove from heat and discard the thyme sprig. Carefully transfer the soup to a blender (or use an immersion blender) and blend until smooth and creamy.

Return the soup to the pot and stir in heavy cream (if using). Season with salt and pepper to taste. Heat gently until warmed through, but do not boil.

Ladle the soup into bowls and garnish with toasted hazelnuts. Serve immediately.