Prepare the ingredients: Clean the celery, chop the stalk and root parts into large pieces. Immediately place them in lemon water. Peel and dice the potato.
Sauté the onion: Heat 3 tablespoons of olive oil in a pot. Sauté the finely chopped onion over low heat for 5-6 minutes until softened. Add the crushed garlic and cook for another 1 minute.
Add the vegetables: Remove the celery from the lemon water and add it to the pot along with the potato. Sauté for 2-3 minutes.
Cook: Add 6 cups of water or vegetable broth. Once it starts boiling, reduce the heat to low and cook for 20-25 minutes until the vegetables are tender.
Blend: Add 3 tablespoons of lemon juice. Blend with an immersion blender until smooth. Add salt.
Serve: Pour into bowls. Drizzle with the remaining olive oil. Garnish with fresh celery leaves and serve hot.
Place the celery in lemon water immediately after chopping, as its color darkens quickly. The stalk of celery has a milder flavor, while the root has a more intense aroma; using both creates a balanced taste.