Preheat the oven to 400 degrees.

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.

Sauté 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. 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.

* For those of you who have graduated to milk, you can add 1 cup of heavy cream prior to pureeing the soup.