How to Make It
In a large pot, cover the potatoes with water, add salt and bring to a boil. Cook the potatoes over moderately high heat until fork-tender, about 25 minutes.
Meanwhile, set a steamer basket in a large saucepan with 1/2 inch of boiling water. Add the fennel, cover and steam over moderate heat until tender, about 12 minutes. Transfer the fennel to a blender or food processor. Add the half-and-half and olive oil, and puree.
Drain the potatoes and return them to the pot. Shake the potatoes over high heat until thoroughly dry. Working over a large bowl, mash the potatoes through a ricer. Stir in the fennel puree, season with salt and pepper and serve.