Place a large stockpot over medium heat. Sprinkle the bottom with a pinch of salt and heat for 1 minute. Add the oil and heat for 30 seconds, being careful not to let it smoke. This creates a nonstick effect.
Add the celery root, celery and onion and saute for 6-10 minutes, stirring often until soft but not brown. Add the stock and bay leaf, bring to a boil, then reduce the heat and simmer for 30 minutes. Add the cashew cream and simmer for an additional 10 minutes.
Remove the bay leaf. Use an immersion blender to blend the soup, or, working in batches carefully pour small portions of soup into a blender, cover carefully (you may want to allow soup to cool before blending), and blend on high. Season with salt and pepper to taste. Ladle into bowls. Place a spoonful of the diced apple in the center of each serving, drizzle the chive oil around the apple and serve.
Put the cashews in a bowl and add cold water to cover them. Cover the bowl and refrigerate overnight.
Drain the cashews and rinse under cold water. Place in a blender with enough fresh cold water to just cover them. Blend on high for several minutes until very smooth.
Blanch the chives for 30 seconds in boiling water, then drain and chill in an ice bath. Drain, wrap the chives in a towel, and squeeze the moisture out.
Place the chives in a blender with the remaining ingredients and blend for 2 minutes; strain through a fine mesh sieve. Put the chive oil in a plastic squeeze bottle with a small opening or use a spoon for drizzling it on the soup.