Lightly coat an unheated medium saucepan with nonstick cooking spray. Preheat pan over medium heat. Add leeks and garlic; cook until tender. Add sweet potato, assorted root vegetables, and chicken broth. Bring to boiling; reduce heat. Cover and simmer about 20 minutes or until vegetables are tender.
Remove from heat. Stir in evaporated milk, fennel seeds, and the ⅛ teaspoon pepper. Transfer to a 1- ½- to 2-quart airtight storage container. Cover and chill overnight.
To serve, transfer mixture to a medium saucepan. Heat through, but do not boil. Pack in four preheated (see Tip) insulated thermal containers. Serve within 5 hours. If desired, sprinkle with additional pepper.
Tip: To preheat, pour boiling water into thermal containers. Let stand, covered, for 5 minutes. Drain and fill with hot soup.