In a large saucepan, heat olive oil over medium-high heat. Add onions, and saute until translucent, 3 to 5 minutes. Add carrots and parsnips, stir to combine. Add tomatoes and stock, stir to combine. Bring to a boil, and reduce to simmer.
Add bouquet garni, turnips, butternut squash, and salt and pepper, to taste. Stir to combine. Cover, and cook until vegetables are fork tender, about 25 minutes.
Add turnip greens and fennel. Cook until greens are wilted, 3 to 5 minutes. Adjust seasoning by adding salt and pepper to taste. Divide the polenta among 6 bowls, and serve immediately, topped with the Fall Ragout.
5 cups homemade chicken stock, or low-sodium canned chicken broth, skimmed of fat
1 1/3 cups quick-cooking polenta
1 tablespoon unsalted butter
1 teaspoon salt
In a medium saucepan, bring stock or 5 cups water to a boil. While whisking rapidly, add the polenta in a thin steady stream. Reduce heat to low, and cook polenta, stirring occasionally, 4 to 5 minutes. Stir in butter and salt during the last minute of cooking. Serve immediately (the polenta thickens significantly as it rests).