1 small peeled, seeded butternut squash
3 medium Yukon Gold potatoes
2 each large carrots and parsnips, peeled
15 to 20 garlic cloves, peeled
¼ cup olive oil, divided
2-½ teaspoons kosher salt, divided
1-½ teaspoons freshly ground black pepper, divided
1 pound ground turkey (not breast only)
1 tablespoon fennel seeds
1 egg, lightly beaten
2 large leeks, cut into ¾-inch slices and rinsed
1 large bulb fennel, cut into ¼-inch slices (reserve feathery fronds for garnish)
8 cups reduced-sodium or homemade chicken broth
Preheat oven to 425° degrees. Cut squash, potatoes, carrots, and parsnips into 1-inch pieces and put in a large oiled roasting pan; add garlic. Toss with 2-½ tablespoons olive oil, 1-½ teaspoons salt and 1 teaspoon pepper and spread out in a single layer, leaving as much room as possible around the pieces. Roast vegetables on lower rack about 40 minutes, or until browned and tender (stir after they’ve browned underneath, about 25 minutes).
Meanwhile, make meatballs. With wet hands, mix turkey, fennel seeds, egg, 1 teaspoon salt, and ½ teaspoon pepper together in a small bowl. Oil your hands with some of remaining oil. Shape turkey mixture into 1-inch meatballs and set them on an oiled rimmed baking sheet as you go, using more oil as needed to coat them well. Roast meatballs on upper rack 15 to 20 minutes, turning a couple of times to brown well on all sides.
Heat 1 tablespoon olive oil in a large pot over medium-heat. Add leeks and fennel, season with salt and pepper to taste, and cook until softened, about 5 minutes. Pour in broth and bring to a boil over high heat, covered. Lower heat and simmer vegetables until meltingly soft, about 25 minutes.
When vegetables in oven have caramelized and meatballs are browned, remove both from oven. Transfer meatballs to roasting pan. Pour a ladleful of hot broth into baking sheet and scrape up browned bits, pour into roasting pan along with all contents of pot and gently scrape up vegetables browned bits. Return to oven and bake 5 minutes to let flavors mingle.