Melt butter in a medium nonstick skillet over medium heat. Add onion; sauté 5 minutes or until lightly browned. Combine onion, sweet potato, next 4 ingredients (through pepper), and 1/4 cup cheese in a large bowl, tossing to coat with flour. Coat a 4-quart electric slow cooker with cooking spray. Transfer vegetable mixture to slow cooker.
Pour broth over potato mixture. Sprinkle with remaining 1/4 cup cheese. Cover and cook on LOW for 4 hours or until potato is tender.
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