Make the topping: Toast the walnuts in a dry pan on medium heat until fragrant. Add butter, honey, and a pinch of salt, and stir until thickened, stirring in cranberries towards the end. Remove from heat and place mixture onto parchment to dry. Break up before garnishing.
Heat olive oil in a large saucepan over medium heat. Add carrot, onion, celery, and a pinch of salt and pepper. Sautee for 5 minutes.
Add celeriac and apple and sautee until celeriac is softened, 10 minutes.
Add broth, bring to a boil, and reduce to a simmer for 10-15 minutes more to fully soften the celery root.
Blend the soup: Use an immersion blender in the saucepan until smooth, or pour soup into a VENTILATED blender and puree until smooth.
Serve warm, and garnish with cranberry walnut topping, if using.
Recipe by at https://goodwitchkitchen.net/celeriac-apple-soup-cranberry-walnut-topping/