Roasting the potatoes gives this soup a special touch.
Preheat the oven to 400ºF.
In a large bowl, toss the potatoes with 1/4 cup olive oil, garlic, salt, and pepper. Spread on a baking sheet and roast for 30 minutes, until cooked through.
Saute the onions and fennel with 2 tablespoons olive oil in a large stockpot on medium heat until translucent, 10 to 15 minutes. Add the roasted potatoes (including the scrapings from the pan) and the chicken stock. Cover and bring to a boil. Lower the heat and simmer uncovered for 1 hour, until all of the vegetables are very soft. Add the heavy cream and allow the soup to cool slightly. Pass the soup through the largest disk of a food mill or chop coarsely in batches in a food processor fitted with a metal blade. Taste for salt and pepper. Reheat and serve hot.