Pour 2 inches of water in a pot and let simmer. Cook fennel, potato, and onion 15 minutes or until vegetables are soft. Strain well.
Using a food processor or blender, puree vegetables until smooth. Pour mixture into a frying pan and cook over medium to medium-low heat 15 minutes or until the mixture becomes thick (do not let brown).
Using electric beaters, mix margarine and half-and-half into fennel mixture to make creamy. Sprinkle with salt and pepper and top with paprika.