1. Cook bacon in a Dutch oven or stockpot until crisp. Remove strips, crumble, and drain on paper towels.
2. Melt butter with drippings over medium-high heat. Add onion and next 5 ingredients, and cook 5 minutes or until tender.
3. Stir in chicken broth, cider vinegar, and sugar. Gradually add kale, and cook, stirring occasionally, 8 to 10 minutes or just until wilted. Reduce heat to medium, and cook, stirring occasionally, 30 minutes or until completely tender.
4. Stir in reserved bacon; season with hot sauce, if desired.