# Wash the celeries, decorticate and dice them. Pell the onion
and dice it finely.
# Put sunflower oil into the pot and make it hot over medium heat. Then, add the celery
on it. Roast the mixture, until the celeries turn to transparent.
# Add 5 cups of water or broth onto the roasted vegetables. Cook the mixture, until the celeries soften totally over medium heat. (About 20-25 minutes.)
# Meanwhile, prepare the liaison of the soup. Whisk the mixture of lemon
and egg in a bowl.
# Add the liaison into the cooking soup at once and stir the soup urgently.
# Stir the soup constantly until it reaches to the boiling temperature. Then, turn the heat to low, and add salt in it. Cook it for 5 more minutes by stirring time to time.
# Add black pepper
into the soup, before removing it from the stove. Fill it into service paltes and garnish with sliced parsley.