Fill a deep saucepan with water and pour over high heat. Wash the fennel and slice it. Peel the potato and chop it coarsely. When the water boils add the fennel and the potato. Cook about 15 minutes or until the fennel is soft. The potato will be almost soft too. Dry the vegetables by dividing them in two dishes. Keep 1 cup of the still warm water. Pour the fennel in the blender and bled on high speed to reduce it in pure. Wash the same saucepan where you cooked the vegetables, dry it, pour the olive oil on the bottom of the saucepan and pour over high head. When it's warm enough, add the onion and a few drops of warm water. Cover and cook on high heat, stirring occasionally about a minute until it's soft, add the potato, stir with a wooden spoon. Add the fennel pure and the water. Add the salt (depends of how salted you like your dishes), the black paper and the white paper. Stir, cover and reduce the heat at low. Cook about 15-20 minutes more. Remove from heat. At this point fresh parsley coarsely chopped can be added. My uncle who is a chef told me that the parsley should be added at the end, just before serving because in this way it keeps it's taste and smell fresh.
Divide the soup into a serving dishes and serve with grilled bread slices.
Makes two servings.