For the celery soup with bacon, clean and wash celery. Peel and wash potato and cut both into small pieces. Peel and dice shallot. Peel apple, remove core and cut into small pieces.
Leave butter in a saucepan. Sauté onion cubes until translucent. Add celery, potato and apple pieces and sauté briefly. Deglaze with vegetable stock, add bay leaf, and bring to a boil. Cover and simmer for about 15 minutes.
During this time, dice bacon and fry in vegetable oil until crispy. Remove the soup pot from the heat. Remove bay leaf from soup.
Add whipping cream and finely puree the celery soup with a hand blender. Stir in bacon. Wash the parsley, dab dry, put aside a few leaves for decoration, finely chop the rest of the herbs and add to the soup.
Bring the soup to the boil again and season with sea salt, pepper and piment d’Espelette. Pour the soup into soup bowls and garnish with apple slices and parsley.