1. Cook bacon and onion in a large Dutch oven over medium heat 5 to 7 minutes. Add brown sugar, and cook, stirring occasionally, 1 to 2 minutes or until sugar is dissolved. Stir in lima beans and butter until butter is melted and beans are thoroughly coated. Stir in 12 cups water.
2. Bring to a boil over medium-high heat; reduce heat to low, and simmer, stirring occasionally, 2 hours or until beans are very tender and liquid is thickened and just below top of beans. Stir in salt and pepper.